Preprints in GR/QC
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Recent News in General Relativity and Quantum Cosmology (gr-qc)
Formation and Decay of Oscillons in Einstein-Cartan Higgs Inflation
Javier Rubio
Published: 2026-03-19
Categories: hep-ph
We review recent progress in the understanding of the preheating stage of Higgs inflation formulated within the Einstein-Cartan framework of gravity. This setup smoothly interpolates between the metric and Palatini formulations of the theory, leading to a distinctive phenomenology in an intermediate regime. Following the end of inflation, the Higgs field undergoes a non-trivial out-of-equilibrium evolution driven by tachyonic instabilities and nonlinear self-interactions, which fragment the inflaton condensate and give rise to well-localized oscillon configurations. While early studies suggested the formation of long-lived oscillons and the possibility of an extended matter-dominated phase, more recent analyses show that self-interactions at small field values render these objects transient, eventually triggering their decay and the onset of radiation domination. We discuss the implications of this dynamics for the thermal history of the Universe, the inflationary observables, and the generation of stochastic gravitational waves.
Quasinormal Modes of Extremal Reissner-Nordstrom Black Holes via Seiberg-Witten Quantization
Yi-Rong Wang, Peng Yang, Kilar Zhang
Published: 2026-03-19
Categories: hep-th
We study the neutral scalar perturbations of asymptotically flat extremal Reissner-Nordström black holes via the quantum geometry of $\mathcal{N}=2$ $\mathrm{SU(2)}$ gauge theory with $N_f=2$ flavors. The master equation, given by a double confluent Heun equation, is mapped to the quantum Seiberg-Witten curve in the Nekrasov-Shatashvili limit. We compute the quasinormal mode frequencies non-perturbatively using the quantization condition derived from the Nekrasov-Shatashvili free energy. Our analytical results accurately reproduce the numerical benchmarks for massless fields, and capture the quasi-resonance behavior of massive probes at the strict extremal limit.
Black hole superradiance in Poincaré gauge theory
Sebastian Bahamonde, Jorge Gigante Valcarcel
Published: 2026-03-19
Categories: gr-qc
We investigate the phenomenon of black hole superradiance in the presence of torsion within the framework of Poincaré gauge theory. In particular, in contrast to the classical approach of General Relativity, we show that the inclusion of torsion in the space-time geometry enables the energy extraction from rotating black holes by Dirac fermions via chiral asymmetry, while preserving the Pauli exclusion principle.
Scalar field in Bianchi type-I cosmology with Lyra's geometry
Evgeny Petuhov, Bijan Saha
Published: 2026-03-19
Categories: gr-qc
In this study, we examine the role of a scalar field in the evolution of the Universe within the framework of a Bianchi type-I cosmological model with Lyra's geometry. Previous research has explored the nonlinear spinor field in various anisotropic and isotropic cosmological models. In our current study, we and dynamical restrictions for Lyra parameters and violation of stress-energy tensor conservation within Lyra geometry. We shown that in considering cases behavior of Lyra's parameter corresponds to relative in?uence in early universe and absence of Lyra geometry in present universe.
Thermodynamic Analysis of Charged AdS Black Holes with Cloud of Strings in Einstein-Bumblebee Gravity via Tsallis Entropy
Faizuddin Ahmed, Edilberto O. Silva
Published: 2026-03-19
Categories: gr-qc
We investigate the thermodynamic properties of charged anti-de Sitter black holes surrounded by a cloud of strings in bumblebee gravity. In this framework, the cloud-of-strings parameter $α$ and the Lorentz-violating parameter $\ell$ modify the horizon structure, the Hawking temperature, the free energies, the specific heat, and the critical behavior in the extended phase-space description. We derive the corresponding equation of state and show that the system exhibits a small--large black-hole phase transition of Van der Waals type. In particular, the critical quantities are deformed by both the cloud of strings and the bumblebee background, while the universal ratio is explicitly altered by Lorentz symmetry breaking. We also examine the Joule--Thomson expansion and analyze the associated inversion and isenthalpic curves, showing how the deformation parameters shift the boundary between heating and cooling regions. In addition, we extend the thermodynamic analysis to a Tsallis entropy-based framework and show that the non-extensive parameter $δ$ significantly changes the temperature profile, stability windows, critical volume, free energies, and sparsity of Hawking radiation. Our results reveal that the combined effects of the string cloud, Lorentz violation, and non-extensive entropy lead to a substantially richer thermodynamic structure than that of the standard Reissner--Nordström--AdS black hole.
GWTC-4.0: Tests of General Relativity. III. Tests of the Remnants
The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration, A. G. Abac, I. Abouelfettouh, F. Acernese, K. Ackley, C. Adamcewicz, S. Adhicary, D. Adhikari, N. Adhikari, R. X. Adhikari, V. K. Adkins, S. Afroz, A. Agapito, D. Agarwal, M. Agathos, N. Aggarwal, S. Aggarwal, O. D. Aguiar, I. -L. Ahrend, L. Aiello, A. Ain, P. Ajith, T. Akutsu, S. Albanesi, W. Ali, S. Al-Kershi, C. Alléné, A. Allocca, S. Al-Shammari, P. A. Altin, S. Alvarez-Lopez, W. Amar, O. Amarasinghe, A. Amato, F. Amicucci, C. Amra, A. Ananyeva, S. B. Anderson, W. G. Anderson, M. Andia, M. Ando, M. Andrés-Carcasona, T. Andrić, J. Anglin, S. Ansoldi, J. M. Antelis, S. Antier, M. Aoumi, E. Z. Appavuravther, S. Appert, S. K. Apple, K. Arai, A. Araya, M. C. Araya, M. Arca Sedda, J. S. Areeda, N. Aritomi, F. Armato, S. Armstrong, N. Arnaud, M. Arogeti, S. M. Aronson, G. Ashton, Y. Aso, L. Asprea, M. Assiduo, S. Assis de Souza Melo, S. M. Aston, P. Astone, F. Attadio, F. Aubin, K. AultONeal, G. Avallone, E. A. Avila, S. Babak, C. Badger, S. Bae, S. Bagnasco, L. Baiotti, R. Bajpai, T. Baka, A. M. Baker, K. A. Baker, T. Baker, G. Baldi, N. Baldicchi, M. Ball, G. Ballardin, S. W. Ballmer, S. Banagiri, B. Banerjee, D. Bankar, T. M. Baptiste, P. Baral, M. Baratti, J. C. Barayoga, B. C. Barish, D. Barker, N. Barman, P. Barneo, F. Barone, B. Barr, L. Barsotti, M. Barsuglia, D. Barta, A. M. Bartoletti, M. A. Barton, I. Bartos, A. Basalaev, R. Bassiri, A. Basti, M. Bawaj, P. Baxi, J. C. Bayley, A. C. Baylor, P. A. Baynard, M. Bazzan, V. M. Bedakihale, F. Beirnaert, M. Bejger, D. Belardinelli, A. S. Bell, D. S. Bellie, L. Bellizzi, W. Benoit, I. Bentara, J. D. Bentley, M. Ben Yaala, S. Bera, F. Bergamin, B. K. Berger, S. Bernuzzi, M. Beroiz, C. P. L. Berry, D. Bersanetti, T. Bertheas, A. Bertolini, J. Betzwieser, D. Beveridge, G. Bevilacqua, N. Bevins, S. Bhagwat, R. Bhandare, R. Bhatt, D. Bhattacharjee, S. Bhattacharyya, S. Bhaumik, V. Biancalana, A. Bianchi, I. A. Bilenko, G. Billingsley, A. Binetti, S. Bini, C. Binu, S. Biot, O. Birnholtz, S. Biscoveanu, A. Bisht, M. Bitossi, M. -A. Bizouard, S. Blaber, J. K. Blackburn, L. A. Blagg, C. D. Blair, D. G. Blair, N. Bode, N. Boettner, G. Boileau, M. Boldrini, G. N. Bolingbroke, A. Bolliand, L. D. Bonavena, R. Bondarescu, F. Bondu, E. Bonilla, M. S. Bonilla, A. Bonino, R. Bonnand, A. Borchers, V. Boschi, S. Bose, V. Bossilkov, Y. Bothra, A. Boudon, L. Bourg, M. Boyle, A. Bozzi, C. Bradaschia, P. R. Brady, A. Branch, M. Branchesi, I. Braun, T. Briant, A. Brillet, M. Brinkmann, P. Brockill, E. Brockmueller, A. F. Brooks, B. C. Brown, D. D. Brown, M. L. Brozzetti, S. Brunett, G. Bruno, R. Bruntz, J. Bryant, Y. Bu, F. Bucci, J. Buchanan, O. Bulashenko, T. Bulik, H. J. Bulten, A. Buonanno, K. Burtnyk, R. Buscicchio, D. Buskulic, C. Buy, R. L. Byer, G. S. Cabourn Davies, R. Cabrita, V. Cáceres-Barbosa, L. Cadonati, G. Cagnoli, C. Cahillane, A. Calafat, T. A. Callister, E. Calloni, S. R. Callos, M. Canepa, G. Caneva Santoro, K. C. Cannon, H. Cao, L. A. Capistran, E. Capocasa, E. Capote, G. Capurri, G. Carapella, F. Carbognani, M. Carlassara, J. B. Carlin, T. K. Carlson, M. F. Carney, M. Carpinelli, G. Carrillo, J. J. Carter, G. Carullo, A. Casallas-Lagos, J. Casanueva Diaz, C. Casentini, S. Y. Castro-Lucas, S. Caudill, M. Cavaglià, R. Cavalieri, A. Ceja, G. Cella, P. Cerdá-Durán, E. Cesarini, N. Chabbra, W. Chaibi, A. Chakraborty, P. Chakraborty, S. Chakraborty, S. Chalathadka Subrahmanya, J. C. L. Chan, M. Chan, K. Chang, S. Chao, P. Charlton, E. Chassande-Mottin, C. Chatterjee, Debarati Chatterjee, Deep Chatterjee, M. Chaturvedi, S. Chaty, K. Chatziioannou, A. Chen, A. H. -Y. Chen, D. Chen, H. Chen, H. Y. Chen, S. Chen, Yanbei Chen, Yitian Chen, H. P. Cheng, P. Chessa, H. T. Cheung, S. Y. Cheung, F. Chiadini, G. Chiarini, A. Chiba, A. Chincarini, M. L. Chiofalo, A. Chiummo, C. Chou, S. Choudhary, N. Christensen, S. S. Y. Chua, G. Ciani, P. Ciecielag, M. Cieślar, M. Cifaldi, B. Cirok, F. Clara, J. A. Clark, T. A. Clarke, P. Clearwater, S. Clesse, F. Cleva, E. Coccia, E. Codazzo, P. -F. Cohadon, S. Colace, E. Colangeli, M. Colleoni, C. G. Collette, J. Collins, S. Colloms, A. Colombo, C. M. Compton, G. Connolly, L. Conti, T. R. Corbitt, I. Cordero-Carrión, S. Corezzi, N. J. Cornish, I. Coronado, A. Corsi, R. Cottingham, M. W. Coughlin, A. Couineaux, P. Couvares, D. M. Coward, R. Coyne, A. Cozzumbo, J. D. E. Creighton, T. D. Creighton, P. Cremonese, S. Crook, R. Crouch, J. Csizmazia, J. R. Cudell, T. J. Cullen, A. Cumming, E. Cuoco, M. Cusinato, L. V. Da Conceição, T. Dal Canton, S. Dal Pra, G. Dálya, O. Dan, B. D'Angelo, S. Danilishin, S. D'Antonio, K. Danzmann, K. E. Darroch, L. P. Dartez, R. Das, A. Dasgupta, V. Dattilo, A. Daumas, N. Davari, I. Dave, A. Davenport, M. Davier, T. F. Davies, D. Davis, L. Davis, M. C. Davis, P. Davis, E. J. Daw, M. Dax, J. De Bolle, M. Deenadayalan, J. Degallaix, M. De Laurentis, F. De Lillo, S. Della Torre, W. Del Pozzo, A. Demagny, F. De Marco, G. Demasi, F. De Matteis, N. Demos, T. Dent, A. Depasse, N. DePergola, R. De Pietri, R. De Rosa, C. De Rossi, M. Desai, R. DeSalvo, A. DeSimone, R. De Simone, A. Dhani, R. Diab, M. C. Díaz, M. Di Cesare, G. Dideron, T. Dietrich, L. Di Fiore, C. Di Fronzo, M. Di Giovanni, T. Di Girolamo, D. Diksha, J. Ding, S. Di Pace, I. Di Palma, D. Di Piero, F. Di Renzo, Divyajyoti, A. Dmitriev, J. P. Docherty, Z. Doctor, N. Doerksen, E. Dohmen, A. Doke, A. Domiciano De Souza, L. D'Onofrio, F. Donovan, K. L. Dooley, T. Dooney, S. Doravari, O. Dorosh, W. J. D. Doyle, M. Drago, J. C. Driggers, L. Dunn, U. Dupletsa, P. -A. Duverne, D. D'Urso, P. Dutta Roy, H. Duval, S. E. Dwyer, C. Eassa, M. Ebersold, T. Eckhardt, G. Eddolls, A. Effler, J. Eichholz, H. Einsle, M. Eisenmann, M. Emma, K. Endo, R. Enficiaud, L. Errico, R. Espinosa, M. Esposito, R. C. Essick, H. Estellés, T. Etzel, M. Evans, T. Evstafyeva, B. E. Ewing, J. M. Ezquiaga, F. Fabrizi, V. Fafone, S. Fairhurst, A. M. Farah, B. Farr, W. M. Farr, G. Favaro, M. Favata, M. Fays, M. Fazio, J. Feicht, M. M. Fejer, R. Felicetti, E. Fenyvesi, J. Fernandes, T. Fernandes, D. Fernando, S. Ferraiuolo, T. A. Ferreira, F. Fidecaro, A. Fienga, P. Figura, A. Fiori, I. Fiori, E. Finch, M. Fishbach, R. P. Fisher, R. Fittipaldi, V. Fiumara, R. Flaminio, S. M. Fleischer, L. S. Fleming, E. Floden, H. Fong, J. A. Font, F. Fontinele-Nunes, C. Foo, B. Fornal, K. Franceschetti, N. Franchini, F. Frappez, S. Frasca, F. Frasconi, J. P. Freed, Z. Frei, A. Freise, O. Freitas, R. Frey, W. Frischhertz, P. Fritschel, V. V. Frolov, G. G. Fronzé, M. Fuentes-Garcia, S. Fujii, T. Fujimori, P. Fulda, M. Fyffe, B. Gadre, J. R. Gair, S. Galaudage, V. Galdi, R. Gamba, A. Gamboa, S. Gamoji, D. Ganapathy, A. Ganguly, B. Garaventa, J. García-Bellido, C. García-Quirós, J. W. Gardner, K. A. Gardner, S. Garg, J. Gargiulo, X. Garrido, A. Garron, F. Garufi, P. A. Garver, C. Gasbarra, B. Gateley, F. Gautier, V. Gayathri, T. Gayer, G. Gemme, A. Gennai, V. Gennari, J. George, R. George, O. Gerberding, L. Gergely, Archisman Ghosh, Sayantan Ghosh, Shaon Ghosh, Shrobana Ghosh, Suprovo Ghosh, Tathagata Ghosh, J. A. Giaime, K. D. Giardina, D. R. Gibson, C. Gier, S. Gkaitatzis, J. Glanzer, F. Glotin, J. Godfrey, R. V. Godley, P. Godwin, A. S. Goettel, E. Goetz, J. Golomb, S. Gomez Lopez, B. Goncharov, G. González, P. Goodarzi, S. Goode, A. W. Goodwin-Jones, M. Gosselin, R. Gouaty, D. W. Gould, K. Govorkova, A. Grado, V. Graham, A. E. Granados, M. Granata, V. Granata, S. Gras, P. Grassia, J. Graves, C. Gray, R. Gray, G. Greco, A. C. Green, L. Green, S. M. Green, S. R. Green, C. Greenberg, A. M. Gretarsson, H. K. Griffin, D. Griffith, H. L. Griggs, G. Grignani, C. Grimaud, H. Grote, S. Grunewald, D. Guerra, D. Guetta, G. M. Guidi, A. R. Guimaraes, H. K. Gulati, F. Gulminelli, H. Guo, W. Guo, Y. Guo, Anuradha Gupta, I. Gupta, N. C. Gupta, S. K. Gupta, V. Gupta, N. Gupte, J. Gurs, N. Gutierrez, N. Guttman, F. Guzman, D. Haba, M. Haberland, S. Haino, E. D. Hall, E. Z. Hamilton, G. Hammond, M. Haney, J. Hanks, C. Hanna, M. D. Hannam, O. A. Hannuksela, A. G. Hanselman, H. Hansen, J. Hanson, S. Hanumasagar, R. Harada, A. R. Hardison, S. Harikumar, K. Haris, I. Harley-Trochimczyk, T. Harmark, J. Harms, G. M. Harry, I. W. Harry, J. Hart, B. Haskell, C. -J. Haster, K. Haughian, H. Hayakawa, K. Hayama, M. C. Heintze, J. Heinze, J. Heinzel, H. Heitmann, F. Hellman, A. F. Helmling-Cornell, G. Hemming, O. Henderson-Sapir, M. Hendry, I. S. Heng, M. H. Hennig, C. Henshaw, M. Heurs, A. L. Hewitt, J. Heynen, J. Heyns, S. Higginbotham, S. Hild, S. Hill, Y. Himemoto, N. Hirata, C. Hirose, D. Hofman, B. E. Hogan, N. A. Holland, K. Holley-Bockelmann, I. J. Hollows, D. E. Holz, L. Honet, D. J. Horton-Bailey, J. Hough, S. Hourihane, N. T. Howard, E. J. Howell, C. G. Hoy, C. A. Hrishikesh, P. Hsi, H. -F. Hsieh, H. -Y. Hsieh, C. Hsiung, S. -H. Hsu, W. -F. Hsu, Q. Hu, H. Y. Huang, Y. Huang, Y. T. Huang, A. D. Huddart, B. Hughey, V. Hui, S. Husa, R. Huxford, L. Iampieri, G. A. Iandolo, M. Ianni, G. Iannone, J. Iascau, K. Ide, R. Iden, A. Ierardi, S. Ikeda, H. Imafuku, Y. Inoue, G. Iorio, P. Iosif, M. H. Iqbal, J. Irwin, R. Ishikawa, M. Isi, K. S. Isleif, Y. Itoh, M. Iwaya, B. R. Iyer, C. Jacquet, P. -E. Jacquet, T. Jacquot, S. J. Jadhav, S. P. Jadhav, M. Jain, T. Jain, A. L. James, K. Jani, J. Janquart, N. N. Janthalur, S. Jaraba, P. Jaranowski, R. Jaume, W. Javed, A. Jennings, M. Jensen, W. Jia, J. Jiang, H. -B. Jin, G. R. Johns, N. A. Johnson, N. K. Johnson-McDaniel, M. C. Johnston, R. Johnston, N. Johny, D. H. Jones, D. I. Jones, R. Jones, H. E. Jose, P. Joshi, S. K. Joshi, G. Joubert, J. Ju, L. Ju, K. Jung, J. Junker, V. Juste, H. B. Kabagoz, T. Kajita, I. Kaku, V. Kalogera, M. Kalomenopoulos, M. Kamiizumi, N. Kanda, S. Kandhasamy, G. Kang, N. C. Kannachel, J. B. Kanner, S. A. KantiMahanty, S. J. Kapadia, D. P. Kapasi, M. Karthikeyan, M. Kasprzack, H. Kato, T. Kato, E. Katsavounidis, W. Katzman, R. Kaushik, K. Kawabe, R. Kawamoto, D. Keitel, L. J. Kemperman, J. Kennington, F. A. Kerkow, R. Kesharwani, J. S. Key, R. Khadela, S. Khadka, S. S. Khadkikar, F. Y. Khalili, F. Khan, T. Khanam, M. Khursheed, N. M. Khusid, W. Kiendrebeogo, N. Kijbunchoo, C. Kim, J. C. Kim, K. Kim, M. H. Kim, S. Kim, Y. -M. Kim, C. Kimball, K. Kimes, M. Kinnear, J. S. Kissel, S. Klimenko, A. M. Knee, E. J. Knox, N. Knust, K. Kobayashi, S. M. Koehlenbeck, G. Koekoek, K. Kohri, K. Kokeyama, S. Koley, P. Kolitsidou, A. E. Koloniari, K. Komori, A. K. H. Kong, A. Kontos, L. M. Koponen, M. Korobko, X. Kou, A. Koushik, N. Kouvatsos, M. Kovalam, T. Koyama, D. B. Kozak, S. L. Kranzhoff, V. Kringel, N. V. Krishnendu, S. Kroker, A. Królak, K. Kruska, J. Kubisz, G. Kuehn, S. Kulkarni, A. Kulur Ramamohan, Achal Kumar, Anil Kumar, Praveen Kumar, Prayush Kumar, Rahul Kumar, Rakesh Kumar, J. Kume, K. Kuns, N. Kuntimaddi, S. Kuroyanagi, S. Kuwahara, K. Kwak, K. Kwan, S. Kwon, G. Lacaille, D. Laghi, A. H. Laity, E. Lalande, M. Lalleman, P. C. Lalremruati, M. Landry, B. B. Lane, R. N. Lang, J. Lange, R. Langgin, B. Lantz, I. La Rosa, J. Larsen, A. Lartaux-Vollard, P. D. Lasky, J. Lawrence, M. Laxen, C. Lazarte, A. Lazzarini, C. Lazzaro, P. Leaci, L. Leali, Y. K. Lecoeuche, H. M. Lee, H. W. Lee, J. Lee, K. Lee, R. -K. Lee, R. Lee, Sungho Lee, Sunjae Lee, Y. Lee, I. N. Legred, J. Lehmann, L. Lehner, M. Le Jean, A. Lemaître, M. Lenti, M. Leonardi, M. Lequime, N. Leroy, M. Lesovsky, N. Letendre, M. Lethuillier, Y. Levin, K. Leyde, A. K. Y. Li, K. L. Li, T. G. F. Li, X. Li, Y. Li, Z. Li, A. Lihos, E. T. Lin, F. Lin, L. C. -C. Lin, Y. -C. Lin, C. Lindsay, S. D. Linker, A. Liu, G. C. Liu, Jian Liu, F. Llamas Villarreal, J. Llobera-Querol, R. K. L. Lo, J. -P. Locquet, S. C. G. Loggins, M. R. Loizou, L. T. London, A. Longo, D. Lopez, M. Lopez Portilla, M. Lorenzini, A. Lorenzo-Medina, V. Loriette, M. Lormand, G. Losurdo, E. Lotti, T. P. Lott, J. D. Lough, H. A. Loughlin, C. O. Lousto, N. Low, N. Lu, L. Lucchesi, H. Lück, D. Lumaca, A. P. Lundgren, A. W. Lussier, S. Ma, R. Macas, M. MacInnis, D. M. Macleod, I. A. O. MacMillan, A. Macquet, K. Maeda, S. Maenaut, S. S. Magare, R. M. Magee, E. Maggio, R. Maggiore, M. Magnozzi, M. Mahesh, M. Maini, S. Majhi, E. Majorana, C. N. Makarem, D. Malakar, J. A. Malaquias-Reis, U. Mali, S. Maliakal, A. Malik, L. Mallick, A. -K. Malz, N. Man, M. Mancarella, V. Mandic, V. Mangano, B. Mannix, G. L. Mansell, M. Manske, M. Mantovani, M. Mapelli, C. Marinelli, F. Marion, A. S. Markosyan, A. Markowitz, E. Maros, S. Marsat, F. Martelli, I. W. Martin, R. M. Martin, B. B. Martinez, D. A. Martinez, M. Martinez, V. Martinez, A. Martini, J. C. Martins, D. V. Martynov, E. J. Marx, L. Massaro, A. Masserot, M. Masso-Reid, S. Mastrogiovanni, T. Matcovich, M. Matiushechkina, L. Maurin, N. Mavalvala, N. Maxwell, G. McCarrol, R. McCarthy, D. E. McClelland, S. McCormick, L. McCuller, S. McEachin, C. McElhenny, G. I. McGhee, K. B. M. McGowan, J. McIver, A. McLeod, I. McMahon, T. 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Published: 2026-03-19
Categories: gr-qc
This is the third paper of the set recording the results of the suite of tests of general relativity (GR) performed on the signals from the fourth Gravitational-Wave Transient Catalog (GWTC-4.0), where we focus on the remnants of the binary mergers. We examine for the first time 42 events from the first part of the fourth observing run of the LIGO-Virgo-KAGRA detectors, alongside events from the previous observation runs, restricting our analysis to the confident signals, which were measured in at least two detectors and that have false alarm rates $\le 10^{-3} \mathrm{yr}^{-1}$. This paper focuses on seven tests of the coalescence remnants. Three of these are tests of the ringdown and its consistency with the expected quasinormal mode spectrum of a Kerr black hole. Specifically, two tests analyze just the ringdown in the time domain, and the third test analyzes the entire signal in the frequency domain. Four tests allow for the existence of possible echoes arriving after the end of the ringdown, which are not expected in GR. We find overall consistency of the remnants with GR. When combining events by multiplying likelihoods (hierarchically), one analysis finds that the GR prediction lies at the boundary of the $98.6^{+1.4}_{-9.4}\%$ ($99.3^{+0.7}_{-4.5}\%$) credible region, an increase from $93.8^{+6.1}_{-20.0}\%$ ($94.9^{+4.4}_{-18.2}\%$) for GWTC-3.0. Here the ranges of values comes from bootstrapping to account for the finite number of events analyzed and suggest that some of the apparently significant deviation could be attributed to variance due to the finite catalog. Since the significance also decreases to 92.2% (96.2%) when including the more recent very loud event GW250114, there is no strong evidence for a GR deviation. We find no evidence for post-merger echoes in the events that were analyzed. (Abridged)
GWTC-4.0: Tests of General Relativity. II. Parameterized Tests
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Published: 2026-03-19
Categories: gr-qc
In this second of three papers on tests of general relativity (GR) applied to the compact binary coalescence signals in the fourth Gravitational-Wave Transient Catalog (GWTC-4.0), we present the results of the parameterized tests of GR and constraints on line-of-sight acceleration. We include events up to and including the first part of the fourth observing run (O4a) of the LIGO Virgo KAGRA detectors. As in the other two papers in this series, we restrict our analysis to the 42 confident signals, measured by at least two detectors, that have false alarm rates $\le 10^{-3} \mathrm{yr}^{-1}$ from O4a, in addition to the 49 such events from previous observing runs. This paper focuses on the eight tests that constrain parameterized deviations from the expected GR (or unaccelerated) values. These include modifications of post-Newtonian (PN) parameters, spin-induced quadrupole moments different from those of a binary black hole, and possible dispersive or birefringent propagation effects. Overall, we find no evidence for physics beyond GR, for spin-induced quadrupole moments different from those of a Kerr black hole in GR, or for line of sight acceleration, with more than 90% of the events including the null result (no deviation) within their 90% credible intervals. We discuss possible systematics affecting the other events and tests, even though they are statistically not surprising, given noise. We improve the bounds on deviations from the GR PN coefficients by factors of 1.2-5.5 and provide illustrative translations to constraints on some modified theories. Also, we update the bound on the mass of the graviton, at 90% credibility, to $m_g \leq 1.92\times 10^{-23} \mathrm{eV}/c^2$. Thus, we see that GR holds, and many of the bounds on possible deviations derived from our events are the best to date.
GWTC-4.0: Tests of General Relativity. I. Overview and General Tests
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Lalande, M. Lalleman, P. C. Lalremruati, M. Landry, B. B. Lane, R. N. Lang, J. Lange, R. Langgin, B. Lantz, I. La Rosa, J. Larsen, A. Lartaux-Vollard, P. D. Lasky, J. Lawrence, M. Laxen, C. Lazarte, A. Lazzarini, C. Lazzaro, P. Leaci, L. Leali, Y. K. Lecoeuche, H. M. Lee, H. W. Lee, J. Lee, K. Lee, R. -K. Lee, R. Lee, Sungho Lee, Sunjae Lee, Y. Lee, I. N. Legred, J. Lehmann, L. Lehner, M. Le Jean, A. Lemaître, M. Lenti, M. Leonardi, M. Lequime, N. Leroy, M. Lesovsky, N. Letendre, M. Lethuillier, Y. Levin, K. Leyde, A. K. Y. Li, K. L. Li, T. G. F. Li, X. Li, Y. Li, Z. Li, A. Lihos, E. T. Lin, F. Lin, L. C. -C. Lin, Y. -C. Lin, C. Lindsay, S. D. Linker, A. Liu, G. C. Liu, Jian Liu, F. Llamas Villarreal, J. Llobera-Querol, R. K. L. Lo, J. -P. Locquet, S. C. G. Loggins, M. R. Loizou, L. T. London, A. Longo, D. Lopez, M. Lopez Portilla, M. Lorenzini, A. Lorenzo-Medina, V. Loriette, M. Lormand, G. Losurdo, E. Lotti, T. P. Lott, J. D. Lough, H. A. Loughlin, C. O. Lousto, N. Low, N. Lu, L. Lucchesi, H. Lück, D. Lumaca, A. P. Lundgren, A. W. Lussier, R. Macas, M. MacInnis, D. M. Macleod, I. A. O. MacMillan, A. Macquet, K. Maeda, S. Maenaut, S. S. Magare, R. M. Magee, E. Maggio, R. Maggiore, M. Magnozzi, M. Mahesh, M. Maini, S. Majhi, E. Majorana, C. N. Makarem, D. Malakar, J. A. Malaquias-Reis, U. Mali, S. Maliakal, A. Malik, L. Mallick, A. -K. Malz, N. Man, M. Mancarella, V. Mandic, V. Mangano, B. Mannix, G. L. Mansell, M. Manske, M. Mantovani, M. Mapelli, C. Marinelli, F. Marion, A. S. Markosyan, A. Markowitz, E. Maros, S. Marsat, F. Martelli, I. W. Martin, R. M. Martin, B. B. Martinez, D. A. Martinez, M. Martinez, V. Martinez, A. Martini, J. C. Martins, D. V. Martynov, E. J. Marx, L. Massaro, A. Masserot, M. Masso-Reid, S. Mastrogiovanni, T. Matcovich, M. Matiushechkina, L. Maurin, N. Mavalvala, N. Maxwell, G. McCarrol, R. McCarthy, D. E. McClelland, S. McCormick, L. McCuller, S. McEachin, C. McElhenny, G. I. McGhee, K. B. M. McGowan, J. McIver, A. McLeod, I. McMahon, T. McRae, R. McTeague, D. Meacher, B. N. Meagher, R. Mechum, Q. Meijer, A. Melatos, C. S. Menoni, F. Mera, R. A. Mercer, L. Mereni, K. Merfeld, E. L. Merilh, J. R. Mérou, J. D. Merritt, M. Merzougui, C. Messick, B. Mestichelli, M. Meyer-Conde, F. Meylahn, A. Mhaske, A. Miani, H. Miao, C. Michel, Y. Michimura, H. Middleton, D. P. Mihaylov, S. J. Miller, M. Millhouse, E. Milotti, V. Milotti, Y. Minenkov, E. M. Minihan, Ll. M. Mir, L. Mirasola, M. Miravet-Tenés, C. -A. Miritescu, A. Mishra, C. Mishra, T. Mishra, A. L. Mitchell, J. G. Mitchell, S. Mitra, V. P. Mitrofanov, K. Mitsuhashi, R. Mittleman, O. Miyakawa, S. Miyoki, A. Miyoko, G. Mo, L. Mobilia, S. R. P. Mohapatra, S. R. Mohite, M. Molina-Ruiz, M. Mondin, M. Montani, C. J. Moore, D. Moraru, A. More, S. More, C. Moreno, E. A. Moreno, G. Moreno, A. Moreso Serra, S. Morisaki, Y. Moriwaki, G. Morras, A. Moscatello, M. Mould, B. Mours, C. M. Mow-Lowry, L. Muccillo, F. Muciaccia, D. Mukherjee, Samanwaya Mukherjee, Soma Mukherjee, Subroto Mukherjee, Suvodip Mukherjee, N. Mukund, A. Mullavey, H. Mullock, J. Mundi, C. L. Mungioli, M. Murakoshi, P. G. Murray, D. Nabari, S. L. Nadji, A. Nagar, N. Nagarajan, K. Nakagaki, K. Nakamura, H. Nakano, M. Nakano, D. Nanadoumgar-Lacroze, D. Nandi, V. Napolano, P. Narayan, I. Nardecchia, T. Narikawa, H. Narola, L. Naticchioni, R. K. Nayak, L. Negri, A. Nela, C. Nelle, A. Nelson, T. J. N. Nelson, M. Nery, A. Neunzert, S. Ng, T. C. K. Ng, L. Nguyen Quynh, S. A. Nichols, A. B. Nielsen, Y. Nishino, A. Nishizawa, S. Nissanke, W. Niu, F. Nocera, J. Noller, M. Norman, C. North, J. Novak, R. Nowicki, J. F. Nuño Siles, L. K. Nuttall, K. Obayashi, J. Oberling, J. O'Dell, E. Oelker, M. Oertel, G. Oganesyan, T. O'Hanlon, M. Ohashi, F. Ohme, R. Oliveri, R. Omer, B. O'Neal, M. Onishi, K. Oohara, B. O'Reilly, M. Orselli, R. O'Shaughnessy, S. O'Shea, S. Oshino, C. Osthelder, I. Ota, D. J. Ottaway, A. Ouzriat, H. Overmier, B. J. Owen, R. Ozaki, A. E. Pace, R. Pagano, M. A. Page, A. Pai, L. Paiella, A. Pal, S. Pal, M. A. Palaia, M. Pálfi, P. P. Palma, C. Palomba, P. Palud, H. Pan, J. Pan, K. C. Pan, P. K. Panda, Shiksha Pandey, Swadha Pandey, P. T. H. Pang, F. Pannarale, K. A. Pannone, B. C. Pant, F. H. Panther, M. Panzeri, F. Paoletti, A. Paolone, A. Papadopoulos, E. E. Papalexakis, L. Papalini, G. Papigkiotis, A. Paquis, A. Parisi, B. -J. Park, J. Park, W. Parker, G. Pascale, D. Pascucci, A. Pasqualetti, R. Passaquieti, L. Passenger, D. Passuello, O. Patane, A. V. Patel, D. Pathak, A. Patra, B. Patricelli, B. G. Patterson, K. Paul, S. Paul, E. Payne, T. Pearce, M. Pedraza, A. Pele, F. E. Peña Arellano, X. Peng, Y. Peng, S. Penn, M. D. Penuliar, A. Perego, Z. Pereira, C. Périgois, G. Perna, A. Perreca, J. Perret, S. Perriès, J. W. Perry, D. Pesios, S. Peters, S. Petracca, C. Petrillo, H. P. Pfeiffer, H. Pham, K. A. Pham, K. S. Phukon, H. Phurailatpam, M. Piarulli, L. Piccari, O. J. Piccinni, M. Pichot, M. Piendibene, F. Piergiovanni, L. Pierini, G. Pierra, V. Pierro, M. Pietrzak, M. Pillas, F. Pilo, L. Pinard, I. M. Pinto, M. Pinto, B. J. Piotrzkowski, M. Pirello, M. D. Pitkin, A. Placidi, E. Placidi, M. L. Planas, W. Plastino, C. Plunkett, R. Poggiani, E. Polini, J. Pomper, L. Pompili, J. Poon, E. Porcelli, E. K. Porter, C. Posnansky, R. Poulton, J. Powell, G. S. Prabhu, M. Pracchia, B. K. Pradhan, T. Pradier, A. K. Prajapati, K. Prasai, R. Prasanna, P. Prasia, G. Pratten, G. Principe, G. A. Prodi, P. Prosperi, P. Prosposito, A. C. Providence, A. Puecher, J. Pullin, P. Puppo, M. Pürrer, H. Qi, J. Qin, G. Quéméner, V. Quetschke, P. J. Quinonez, N. Qutob, R. Rading, I. Rainho, S. Raja, C. Rajan, B. Rajbhandari, K. E. Ramirez, F. A. Ramis Vidal, M. Ramos Arevalo, A. Ramos-Buades, S. Ranjan, K. Ransom, P. Rapagnani, B. Ratto, A. Ravichandran, A. Ray, V. Raymond, M. Razzano, J. Read, T. Regimbau, S. Reid, C. Reissel, D. H. Reitze, A. I. Renzini, B. Revenu, A. Revilla Peña, R. Reyes, L. Ricca, F. Ricci, M. Ricci, A. Ricciardone, J. Rice, J. W. Richardson, M. L. Richardson, A. Rijal, K. Riles, H. K. Riley, S. Rinaldi, J. Rittmeyer, C. Robertson, F. Robinet, M. Robinson, A. Rocchi, L. Rolland, J. G. Rollins, A. E. Romano, R. Romano, A. Romero, I. M. Romero-Shaw, J. H. Romie, S. Ronchini, T. J. Roocke, L. Rosa, T. J. Rosauer, C. A. Rose, D. Rosińska, M. P. Ross, M. Rossello-Sastre, S. Rowan, S. K. Roy, S. Roy, D. Rozza, P. Ruggi, N. Ruhama, E. Ruiz Morales, K. Ruiz-Rocha, S. Sachdev, T. Sadecki, P. Saffarieh, S. Safi-Harb, M. R. Sah, S. Saha, T. Sainrat, S. Sajith Menon, K. Sakai, Y. Sakai, M. Sakellariadou, S. Sakon, O. S. Salafia, F. Salces-Carcoba, L. Salconi, M. Saleem, F. Salemi, M. Sallé, S. U. Salunkhe, S. Salvador, A. Salvarese, A. Samajdar, A. Sanchez, E. J. Sanchez, L. E. Sanchez, N. Sanchis-Gual, J. R. Sanders, E. M. Sänger, F. Santoliquido, F. Sarandrea, T. R. Saravanan, N. Sarin, P. Sarkar, A. Sasli, P. Sassi, B. Sassolas, B. S. Sathyaprakash, R. Sato, S. Sato, Yukino Sato, Yu Sato, O. Sauter, R. L. Savage, T. Sawada, H. L. Sawant, S. Sayah, V. Scacco, D. Schaetzl, M. Scheel, A. Schiebelbein, M. G. Schiworski, P. Schmidt, S. Schmidt, R. Schnabel, M. Schneewind, R. M. S. Schofield, K. Schouteden, B. W. Schulte, B. F. Schutz, E. Schwartz, M. Scialpi, J. Scott, S. M. Scott, R. M. Sedas, T. C. Seetharamu, M. Seglar-Arroyo, Y. Sekiguchi, D. Sellers, N. Sembo, A. S. Sengupta, E. G. Seo, J. W. Seo, V. Sequino, M. Serra, A. Sevrin, T. Shaffer, U. S. Shah, M. A. Shaikh, L. Shao, A. K. Sharma, Preeti Sharma, Prianka Sharma, Ritwik Sharma, S. Sharma Chaudhary, P. Shawhan, N. S. Shcheblanov, E. Sheridan, Z. -H. Shi, M. Shikauchi, R. Shimomura, H. Shinkai, S. Shirke, D. H. Shoemaker, D. M. Shoemaker, R. W. Short, S. ShyamSundar, A. Sider, H. Siegel, D. Sigg, L. Silenzi, L. Silvestri, M. Simmonds, L. P. Singer, Amitesh Singh, Anika Singh, D. Singh, M. K. Singh, N. Singh, S. Singh, A. M. Sintes, V. Sipala, V. Skliris, B. J. J. Slagmolen, D. A. Slater, T. J. Slaven-Blair, J. Smetana, J. R. Smith, L. Smith, R. J. E. Smith, W. J. Smith, S. Soares de Albuquerque Filho, M. Soares-Santos, K. Somiya, I. Song, S. Soni, V. Sordini, F. Sorrentino, H. Sotani, F. Spada, V. Spagnuolo, A. P. Spencer, P. Spinicelli, A. K. Srivastava, F. Stachurski, C. J. Stark, D. A. Steer, J. Steinhoff, N. Steinle, J. Steinlechner, S. Steinlechner, N. Stergioulas, P. Stevens, M. StPierre, M. D. Strong, A. Strunk, A. L. Stuver, M. Suchenek, S. Sudhagar, Y. Sudo, N. Sueltmann, L. Suleiman, K. D. Sullivan, J. Sun, L. Sun, S. Sunil, J. Suresh, B. J. Sutton, P. J. Sutton, K. Suzuki, M. Suzuki, S. Swain, B. L. Swinkels, A. Syx, M. J. Szczepańczyk, P. Szewczyk, M. Tacca, H. Tagoshi, S. C. Tait, K. Takada, H. Takahashi, R. Takahashi, A. Takamori, S. Takano, H. Takeda, K. Takeshita, I. Takimoto Schmiegelow, M. Takou-Ayaoh, C. Talbot, M. Tamaki, N. Tamanini, D. Tanabe, K. Tanaka, S. J. Tanaka, S. Tanioka, D. B. Tanner, W. Tanner, L. Tao, R. D. Tapia, E. N. Tapia San Martín, C. Taranto, A. Taruya, J. D. Tasson, J. G. Tau, D. Tellez, R. Tenorio, H. Themann, A. Theodoropoulos, M. P. Thirugnanasambandam, L. M. Thomas, M. Thomas, P. Thomas, J. E. Thompson, S. R. Thondapu, K. A. Thorne, E. Thrane, J. Tissino, A. Tiwari, Pawan Tiwari, Praveer Tiwari, S. Tiwari, V. Tiwari, M. R. Todd, M. Toffano, A. M. Toivonen, K. Toland, A. E. Tolley, T. Tomaru, V. Tommasini, T. Tomura, H. Tong, C. Tong-Yu, A. Torres-Forné, C. I. Torrie, I. Tosta e Melo, E. Tournefier, M. Trad Nery, K. Tran, A. Trapananti, R. Travaglini, F. Travasso, G. Traylor, M. Trevor, M. C. Tringali, A. Tripathee, G. Troian, A. Trovato, L. Trozzo, R. J. Trudeau, T. Tsang, S. Tsuchida, L. Tsukada, K. Turbang, M. Turconi, C. Turski, H. Ubach, N. Uchikata, T. Uchiyama, R. P. Udall, T. Uehara, K. Ueno, V. Undheim, L. E. Uronen, T. Ushiba, M. Vacatello, H. Vahlbruch, N. Vaidya, G. Vajente, A. Vajpeyi, J. Valencia, M. Valentini, S. A. Vallejo-Peña, S. Vallero, V. Valsan, M. van Dael, E. Van den Bossche, J. F. J. van den Brand, C. Van Den Broeck, M. van der Sluys, A. Van de Walle, J. van Dongen, K. Vandra, M. VanDyke, H. van Haevermaet, J. V. van Heijningen, P. Van Hove, J. Vanier, M. VanKeuren, J. Vanosky, N. van Remortel, M. Vardaro, A. F. Vargas, V. Varma, A. N. Vazquez, A. Vecchio, G. Vedovato, J. Veitch, P. J. Veitch, S. Venikoudis, R. C. Venterea, P. Verdier, M. Vereecken, D. Verkindt, B. Verma, Y. Verma, S. M. Vermeulen, F. Vetrano, A. Veutro, A. Viceré, S. Vidyant, A. D. Viets, A. Vijaykumar, A. Vilkha, N. Villanueva Espinosa, V. Villa-Ortega, E. T. Vincent, J. -Y. Vinet, S. Viret, S. Vitale, H. Vocca, D. Voigt, E. R. G. von Reis, J. S. A. von Wrangel, W. E. Vossius, L. Vujeva, S. P. Vyatchanin, J. Wack, L. E. Wade, M. Wade, K. J. Wagner, R. M. Wald, L. Wallace, E. J. Wang, H. Wang, J. Z. Wang, W. H. Wang, Y. F. Wang, G. Waratkar, J. Warner, M. Was, T. Washimi, N. Y. Washington, D. Watarai, B. Weaver, S. A. Webster, N. L. Weickhardt, M. Weinert, A. J. Weinstein, R. Weiss, L. Wen, K. Wette, J. T. Whelan, B. F. Whiting, C. Whittle, E. G. Wickens, D. Wilken, A. T. Wilkin, B. M. Williams, D. Williams, M. J. Williams, N. S. Williams, J. L. Willis, B. Willke, M. Wils, L. Wilson, C. W. Winborn, J. Winterflood, C. C. Wipf, G. Woan, J. Woehler, N. E. Wolfe, H. T. Wong, I. C. F. Wong, K. Wong, T. Wouters, J. L. Wright, M. Wright, B. Wu, C. Wu, D. S. Wu, H. Wu, K. Wu, Q. Wu, Y. Wu, Z. Wu, E. Wuchner, D. M. Wysocki, V. A. Xu, Y. Xu, N. Yadav, H. Yamamoto, K. Yamamoto, T. S. Yamamoto, T. Yamamoto, R. Yamazaki, T. Yan, K. Z. Yang, Y. Yang, Z. Yarbrough, J. Yebana, S. -W. Yeh, A. B. Yelikar, X. Yin, J. Yokoyama, T. Yokozawa, S. Yuan, H. Yuzurihara, M. Zanolin, M. Zeeshan, T. Zelenova, J. -P. Zendri, M. Zeoli, M. Zerrad, M. Zevin, L. Zhang, N. Zhang, R. Zhang, T. Zhang, C. Zhao, J. Zhao, Yue Zhao, Yuhang Zhao, Z. -C. Zhao, Y. Zheng, H. Zhong, H. Zhou, H. O. Zhu, Z. -H. Zhu, A. B. Zimmerman, L. Zimmermann, M. E. Zucker, J. Zweizig
Published: 2026-03-19
Categories: gr-qc
The worldwide LIGO-Virgo-KAGRA network of gravitational-wave (GW) detectors continues to increase in sensitivity, thus increasing the quantity and quality of the detected GW signals from compact binary coalescences. These signals allow us to perform ever-more sensitive tests of general relativity (GR) in the dynamical and strong-field regime of gravity. This paper is the first of three, where we present the results of a suite of tests of GR using the binary signals included in the fourth GW Transient Catalog (GWTC-4.0), i.e., up to and including the first part of the fourth observing run of the detectors (O4a). We restrict our analysis to the 91 confident signals, henceforth called events, that were measured by at least two detectors, and have false alarm rates $\le 10^{-3} \mathrm{yr}^{-1}$. These include 42 events from O4a. This first paper presents an overview of the methods, selection of events and GR tests, and serves as a guidemap for all three papers. Here we focus on the four general tests of consistency, where we find no evidence for deviations from our models. Specifically, for all the events considered, we find consistency of the residuals with noise. The final mass and final spin as inferred from the low- and high-frequency parts of the waveform are consistent with each other. We also find no evidence for deviations from the GR predictions for the amplitudes of subdominant GW multipole moments, or for non-GR modes of polarization. We thus find that GR, without new physics beyond it, is still consistent with these GW events. The results of the two additional papers in this trio also find overall consistency with vacuum GR, with more than 90% of the events being consistent with GR at the 90% credible level. While one of the ringdown analyses finds the GR value in the tails for its combined results, this may be due in part to catalog variance.
Revisiting $f(T)$ Teleparallel Gravity with a Parametrized Hubble Parameter and Observational Constraints
Khomesh R. Patle, G. P. Singh
Published: 2026-03-19
Categories: gr-qc
In this paper, the dynamical behavior of the accelerated expansion of the universe is studied within the framework of $f(T)$ gravity by considering a well-motivated functional form of $f(T)$. A specific form of the Hubble parameter is assumed, which under two different cases, leads to two distinct cosmological models expressed in terms of the redshift parameter $H(z)$, providing insights into cosmic dynamics. These models are employed to explore the expansion history of the universe and the evolution of several cosmological parameters. Using Bayesian statistical techniques based on the $χ^{2}$-minimization method, the median values of the model parameters are determined for both the cosmic chronometer (CC) and the joint (CC + Pantheon) datasets. The evolution of the deceleration parameter, energy density, pressure and the equation of state parameter for dark energy is analyzed. Additionally, the validity of the energy conditions and the nature of the statefinder diagnostic are examined. The present age of the universe is also estimated for the proposed models.
Observational Signatures of Rotating Ayón-Beato-García Black Holes: Shadows, Accretion Disks and Images
Zhenglong Ban, Meng Chen, Rong-Jia Yang
Published: 2026-03-19
Categories: gr-qc
We investigate the shadows, accretion disks, and observational images of rotating Ayón-Beato-García black holes characterized by mass $ M $ , spin $ a $ , and electric charge $ ζ$ . Our analysis reveals that the shadow size decreases with increasing $ ζ$, and in near-extremal configurations (e.g., $ a = 0.95 $), the shadow adopts a distinctive ``D''-shaped morphology. For the accretion disk, we extend its inner edge to the event horizon and account for distinct particle dynamics inside and outside the innermost stable circular orbit (ISCO). We find that the correlation between $ (a, ζ) $ and the observer's inclination angle significantly influences image asymmetry and inner shadow distortion. At higher inclinations, the direct and lensed images separate, forming a hat-like structure. Additionally, we compute the redshift distribution of the disk's direct and lensed emissions under varying parameters and viewing angles. By comparing theoretical shadow diameters with the Event Horizon Telescope observations of M87 $^{*}$ and Sgr A $^{*}$--using inclination angles of $17^{\circ} $, $ 50^{\circ} $, and $ 90^{\circ} $--we constrain the viable parameter space, yielding the joint bound $0.132811\,M < ζ< 0.213607\,M$ consistent with both sources.
Analytic Expressions for Quasinormal Modes of a Regular Black Hole Sourced by a Dehnen-Type Halo
Zainab Malik
Published: 2026-03-19
Categories: gr-qc
Using an expansion beyond the eikonal regime, we derive relatively compact and accurate analytic expressions for the gravitational quasinormal modes of an asymptotically flat black hole supported by a Dehnen-type dark-matter halo. The spacetime admits a simple analytic metric describing a supermassive black hole embedded in a galactic environment, with the lapse function $f(r)=1-\frac{2 M r^{2}}{(r+a)^{3}}.$ The parameter $a$ sets the characteristic scale of the surrounding halo and controls the regularization of the central region. The axial gravitational sector splits into two distinct channels, referred to as the "up" and "down" perturbations, which are not isospectral.
Thermodynamics of Kerr-Bertotti-Robinson black hole
Li Hu, Rong-Gen Cai, Shao-Jiang Wang
Published: 2026-03-19
Categories: gr-qc
We investigate the thermodynamic properties of the Kerr-Bertotti-Robinson black hole, an exact Petrov type D solution of Einstein-Maxwell theory describing a rotating black hole immersed in an external electromagnetic field. While the conserved angular momentum and electric charge can be computed straightforwardly, the conserved mass cannot be obtained through standard integrability methods due to the nontrivial asymptotically uniform external electromagnetic field. To overcome this difficulty, we adopt the Christodoulou-Ruffini mass relation as a thermodynamic definition of the conserved mass, and identify the associated generator, thereby fixing the ambiguity in defining this conserved mass and constructing the thermodynamic potentials. These thermodynamic quantities naturally satisfy the first law of black-hole thermodynamics as well as the Smarr formula.
Exact pp-wave solutions in shift-symmetric higher-order scalar-tensor theories
Masato Minamitsuji
Published: 2026-03-19
Categories: gr-qc
We investigate exact plane-fronted gravitational wave (pp-wave) solutions within the framework of shift-symmetric quadratic-order higher-order scalar--tensor (HOST) theories. These solutions represent fully nonlinear radiative spacetimes that extend beyond the linearized approximation. We demonstrate that under the algebraic conditions on the coupling functions, the gravitational field equations reduce to a two-dimensional Laplace equation for the wave profile, recovering the structural form of vacuum general relativity (GR). By adopting a scalar field ansatz that depends linearly on transverse coordinates and arbitrarily on the retarded null coordinate, we maintain a constant kinetic term of the scalar field. This configuration allows for a \emph{stealth pp-wave} solution, where a nontrivial scalar field profile coexists with the gravitational wave without backreacting on the spacetime geometry. We further show that these stealth configurations are fully compatible with the degeneracy conditions of Class-Ia DHOST theories and satisfy current observational constraints. Finally, we examine the behavior of these solutions under disformal transformations, revealing that while the Brinkmann form is preserved, the stealth property is generically lost due to the mixing of scalar and tensor degrees of freedom. These results establish the robustness of pp-wave solutions in viable DHOST frameworks and highlight their utility for probing nonlinear effects in modified gravity.
Scalarization of charged Taub-NUT black hole and the entropy bound
Lei Zhang, Hai-Shan Liu
Published: 2026-03-19
Categories: gr-qc
We investigate the spontaneous scalarization of charged Taub-NUT black holes within the framework of Einstein-Maxwell-scalar-Gauss-Bonnet gravity. By selecting a suitable coupling function, the theory admits the analytic charged Taub-NUT geometry as a solution. We demonstrate that this scalar-free background becomes unstable within specific parameter regimes, leading to the bifurcation of a new branch of hairy charged Taub-NUT black holes. These solutions are characterized by a two-dimensional parameter space spanned by the electric charge and the NUT parameter. We conduct a systematic study of their properties, specifically the scalar charge, temperature, and entropy. Our analysis reveals that the entropy of the scalarized solutions exhibits particularly compelling features. Two universal characteristics emerge: first, the entropy of the hairy black hole is strictly greater than that of its scalar-free counterpart; second, the entropy reaches a local maximum precisely at the bifurcation point. Notably, when the electric charge is fixed, this maximum entropy value remains universal across a specific range of the mass parameter.
Bosonic and fermionic mutual information of N-partite systems in dilaton black hole background
Xiao-Wei Teng, Rui-Yang Xu, Hui-Chen Yang, Shu-Min Wu
Published: 2026-03-19
Categories: gr-qc
We investigate multipartite quantum correlations by analyzing the mutual information of N-partite states for both free bosonic and fermionic fields in the background of a Garfinkle-Horowitz-Strominger (GHS) dilaton black hole. Focusing on multipartite GHZ and W states, we examine how the Hawking effect influences the N-partite mutual information when one observer hovers near the event horizon while the remaining observers stay in the asymptotically flat region. By tracing over the inaccessible modes inside the event horizon, we derive analytical expressions for the N-partite mutual information in dilaton spacetime for both bosonic and fermionic fields. Our results show that fermionic mutual information is larger than its bosonic counterpart under the influence of the dilaton black hole, whereas the fermionic relative entropy of coherence (REC) is smaller than the bosonic REC. Moreover, the mutual information of GHZ states is consistently larger than that of W states, while the REC of GHZ states is smaller than that of W states in curved spacetime. These findings indicate that the choice of quantum resources should be tailored to the particle species and state structure in relativistic quantum information tasks to optimize their operational efficiency.
On the Finsler variational nature of autoparallels in metric-affine geometry
Lehel Csillag, Nicoleta Voicu, Salah Elgendi, Christian Pfeifer
Published: 2026-03-19
Categories: math-ph
In metric-affine geometry, autoparallels are generically non-variational, i.e., they are not extremals of any action integral. The existence of a parameter-invariant action principle for autoparallels is a longstanding open problem, which is equivalent to the so-called Finsler metrizability of the connection, i.e., to the fact that these autoparallels can be interpreted as Finsler geodesics. In this article, we address this problem for the class of torsion-free affine connections with vectorial nonmetricity, which includes, as notable subcases, Weyl and Schrödinger connections. For this class, we determine the necessary and sufficient conditions for the existence of a Finsler Lagrangian that metrizes the connection and depends only algebraically on it. In the cases where such a Finsler Lagrangian exists, we construct it explicitly. In particular, we show that a broad class of such connections is Finsler metrizable.
Black Hole--Entropy Container or Creator
William G Unruh
Published: 2026-03-19
Categories: gr-qc
Do black holes possess entropy or do they create it? The dominant assumption is that they possess entropy, and a they evaporate that entropy is emitted and decreases. In this paper I use a model of a linear amplifier, in which I argue that the amplifier has not entropy and yet it emits entropy in the process of it operation. This model is closely related to behaviour of black holes, resulting in answer the question of that title that black holes do not have entropy, but nevertheless them create and emit entropy with the total entropy emitted being the same as the usual expression proportional to the square of the mas of the black hole.
Contrasting behaviour of two spherically symmetric perfect fluids near a weak null singularity in a spherically symmetric black hole
Raya V. Mancheva
Published: 2026-03-18
Categories: gr-qc
In this work we contrast the behaviour of two spherically symmetric matter models in a class of spherically symmetric spacetimes which feature a weak null singularity. This class in particular contains spherically symmetric perturbations of subextremal Reissner-Nordström under the Einstein--Maxwell--scalar field system, a system for which a $C^2$ formulation of the strong cosmic censorship conjecture was proved by Luk-Oh, arXiv:1702.05715 and Dafermos, arXiv:1201.1797. Firstly, we consider the Cauchy problem of spherically symmetric dust falling into the weak null singularity (WNS) where the initial dust velocity is normal to a smooth spacelike curve with certain properties. We prove that the flow of the dust velocity does not experience any shell-crossing before or at the singularity, the velocity vector remains timelike, and that the dust energy density remains bounded as matter approaches the singularity. Secondly, we consider the characteristic initial value problem for stiff perfect fluid falling into the WNS. By relating the stiff fluid velocity and energy density to a scalar field satisfying the homogeneous linear wave equation, we prove that this energy density becomes infinite as we approach the weak null singularity. Furthermore, we show that the ingoing component of the stiff fluid velocity blows up while the outgoing component approaches zero at the singularity. Therefore the velocity vector approaches an ingoing null vector tangent to the singular hypersurface.
Holographic Quantum Foam: Theoretical Underpinnings and Observational Evidence
Eric Steinbring, Y. Jack Ng
Published: 2026-03-18
Categories: gr-qc
Spacetime is foamy due to quantum fluctuations. Various gedanken experiments show that distances fluctuate by amounts consistent with the holographic principle, hence the name "holographic quantum foam" (HQF). One important prediction of HQF is that necessarily there exists a dark sector in the universe. The resulting cosmology is found (at least qualitatively) to be consistent with observations. Interestingly the quanta of the dark sector are found not to obey the familiar (fermionic or bosonic) statistics, but the exotic statistics known as infinite statistics (or quantum Boltzmann statistics). The most important challenge now is to check if HQF is consistent with experiments/observations. One way is to look for observational evidence of blurred distant point-sources due to physics at the Planck scale. For over two decades it has been debated whether those tiny inherent uncertainties in time and path-length can accumulate in transiting electromagnetic wavefronts from quasars and Gamma-Ray Bursts (GRBs). But a recent event is special: GRB221009A was extremely bright and energetic. That allowed follow-up across the whole spectrum from the optical/near-infrared through to X-rays, and including the highest-ever-recorded energy gamma-rays; all consistent with blurring by HQF. Those data, and a calculation of the HQF-widened point-spread function (PSF) for real telescopes viewing a GRB are presented.
Robinson-Trautman spacetimes in (2+1) dimensions
Alberto Saa
Published: 2026-03-18
Categories: gr-qc
We propose a Robinson-Trautman evolution in $(2+1)$-dimensional spacetime that retains key structural features of the four-dimensional case. We consider a recently studied exact family of metrics to select a nonstationary geometry with a cosmological constant, sourced by a null fluid. The metric is completely determined by a single positive function $P(u,φ)$, while the corresponding matter content is encoded in a null-fluid density. Motivated by the role of the area-preserving Calabi flow in four dimensions, we introduce a fourth-order length-preserving evolution equation for $P(u,φ)$ whose stationary configurations correspond, for negative cosmological constant, to boosted BTZ black holes. Numerical solutions strongly support the relaxation of generic regular initial data $P(0,φ)$ toward the stationary sector. The resulting system provides a simple toy model for dissipative dynamics driven by null radiation in lower-dimensional gravity, with several structural similarities to phenomena associated with genuine gravitational radiation.
The Steep Price of No Hair in Thiemann Regularized Loop Quantum Cosmology
Meysam Motaharfar, Parampreet Singh
Published: 2026-03-18
Categories: gr-qc
Loop quantum cosmology based on Thiemann's regularization procedure leads to the resolution of the big bang singularity and bounce in the isotropic setting. A key distinction from standard loop quantum cosmology is that, in this framework, either the pre-bounce or post-bounce epoch is necessarily characterized by an emergent Planckian de Sitter phase. In this work we explore the Planckian physics of Thiemann regularized loop quantization of the Bianchi-I spacetimes. We show that as in the isotropic model, there exists an emergent de Sitter phase which naturally dampens anisotropic shear and removes cosmic hair. However, this isotropization comes at a steep price: although a macroscopic post-bounce regime is achieved, the universe never becomes truly classical. We further demonstrate that this isotropization mechanism is non-generic. These results help clarify and reinterpret recent results by Gan et al. [1] that, in anisotropic Thiemann regularized loop quantum cosmology, quantum gravity effects generically damp anisotropic shear in a way that is independent of initial conditions and the matter content, and that this anisotropic shear damping mechanism arises from a novel quantum gravity effect. Our work explains the origin of this mechanism and its limitations.
A menagerie of Schwarzians: coadjoint orbits of Virasoro and near-dS$_2$ quantum gravity
Henry Maxfield
Published: 2026-03-18
Categories: hep-th
The Schwarzian theory, which governs the universal low-energy dynamics of near-extremal black holes and the SYK model, can be characterised as an integral over a particular coadjoint orbit of the Virasoro group. We describe and solve a complete classification of all possible generalised Schwarzian theories, defined by integrals over any Virasoro coadjoint orbit, including new classes of theories with qualitatively novel features. The classification of coadjoint orbits coincides with the moduli space of constant positive curvature two-dimensional Lorentzian geometries, and the associated Schwarzian theories govern associated wavefunctions in asymptotically near-dS$_2$ gravity (Jackiw-Teitelboim gravity in particular). The novel theories are inherently Lorentzian, defined by oscillatory path integrals weighted by $e^{iI}$ and force consideration of varying `coupling functions' (renormalised dilaton) which may not have definite sign. The definition of the theories involves an ambiguity, arising because the operator describing quadratic fluctuations at one loop fails to be essentially self-adjoint. This requires a choice of boundary condition, and also forces us to allow certain singularities in configurations and classical solutions. The choice is justified from the realisation in JT gravity, which naturally regulates these singularities. The path integral remains one-loop exact via fermionic localisation, but this requires additional input beyond the Duistermaat-Heckman theorem. This allows an exact computation of the path integral for all theories and all couplings, including new results for the original Schwarzian theory.
High-Frequency Gravitational Waves from Phase Transitions in Nascent Neutron Stars
Katarina Bleau, Joachim Kopp, Jiheon Lee, Jorinde van de Vis
Published: 2026-03-18
Categories: hep-ph
Tentative evidence suggests that the cores of massive neutron stars consist of deconfined quark matter. We argue that the formation of such a quark matter core during a galactic supernova could be accompanied by the emission of gravitational waves in the MHz band. These signals constitute a new target for high-frequency gravitational wave detectors, demonstrating that such detectors may offer unique opportunities for testing quantum chromodynamics in an otherwise inaccessible regime.
Branching Universes
Anamaria Hell, Tatsuya Daniel
Published: 2026-03-18
Categories: hep-th
We propose the idea that our Universe is a realization among different possible branches, which can be observationally tested through the modified dispersion relation of the gravitational waves. We achieve this through a framework of spatially constrained vector fields. We show that the simplest realizations of such theories in flat and cosmological spacetimes do not introduce new propagating modes, but they give rise to tensor perturbations that differ from those of standard general relativity. We further show that such theories admit stealth black hole solutions, and we recover weak gravitational potentials, thus passing the solar system experiments. Finally, we discuss the implications of such theories and propose further generalizations.
On the Astrophysical Origin of Binary Black Hole Subpopulations: A Tale of Three Channels?
Anarya Ray, Shirsha Mukherjee, Michael Zevin, Vicky Kalogera
Published: 2026-03-18
Categories: astro-ph.HE
There is increasing evidence for multiple binary black hole~(BBH) subpopulations in the cumulative gravitational wave catalog by the LIGO-Virgo-KAGRA Collaboration. The astrophysical interpretation of this complex underlying population is subject to theoretical uncertainties in treatments of binary stellar evolution, core collapse, and host environments. In this \textit{Letter}, using parametrized mixture models, we show that the BBH detection sample comprises three astrophysical subpopulations that are likely dominated by specific formation channels. In particular, we show that the $10M_{\odot}$ peak and the $35M_{\odot}$ feature in the BBH mass spectrum correspond to distinct mass-ratio, spin alignment, spin precession, and redshift evolution properties. We show that mass-based transitions reported in the distribution of BBH parameters naturally emerge from our inferred distributions without explicit modeling. Our results are consistent with the current observed population arising from specific relative abundances of isolated binary evolution, dynamical formation in globular clusters, and higher-generation BBH mergers. Under this interpretation, we constrain the relative underlying fraction of these channels to be $79.0^{+11.5}_{-10.9}\%$, $14.5^{+11.6}_{-8.0}\%$, and, $2.5^{+5.5}_{-1.8}\%$, respectively, and find these relative fractions to be evolving over cosmic time with more than $1σ$ confidence. Our interpretation relies on simple theoretical predictions that are mostly robust against uncertainties in BBH formation, with more definite conclusions expected in the near future.
Observational Signatures of Exact Black Hole Solutions in a Dark Matter Halo
Azalbek Boltaev, Tursunali Xamidov, Sanjar Shaymatov
Published: 2026-03-18
Categories: gr-qc
In this work, we derive novel exact solutions describing Schwarzschild-like black holes (BHs) embedded in a Dehnen-type dark matter (DM) halo density profile and investigate their geometric, dynamical, and observational signatures arising from such geometries. We begin by analyzing the horizon structure and spacetime curvature invariants, as well as examining the energy conditions associated with the DM halo. Subsequently, we study the influence of the DM halo on both timelike and null geodesics in the resulting geometry. Finally, we obtain observational constraints on the DM halo parameters by comparing the model predictions with weak-field data from Mercury and the S2 star orbit, as well as strong-field observations from the Event Horizon Telescope (EHT), GRAVITY, and combined (EHT+GRAVITY) datasets for M87* and Sgr A*, employing Bayesian inference and Markov Chain Monte Carlo (MCMC) methods to determine the best-fit values and corresponding upper limits of the model parameters. Our analysis provides valuable insight into probing the potential influence of DM halo environments on spacetime geometry and observable properties of astrophysical BHs, offering an alternative perspective on BH-DM interactions.
Probing Kerr black hole in a uniform Bertotti-Robinson magnetic field through astrophysical quasi-periodic oscillations
Hamza Rehman, Sanjar Shaymatov, Saddam Hussain, Tao Zhu
Published: 2026-03-18
Categories: astro-ph.HE
In this study, the behavior of high-frequency quasi-periodic oscillations (QPOs) is investigated around a Kerr black hole immersed in a uniform Bertotti-Robinson magnetic field. The motion of the test particle is analyzed by determining the geodesic equations and evaluating the corresponding orbital, radial, and vertical epicyclic frequencies. These fundamental frequencies are used to construct the theoretical framework of QPO models based on parametric and forced resonance mechanisms. Observational data obtained from several black hole X-ray binaries (GRO J1655-40, XTE J1550-564, XTE J1859+226, GRS 1915+105, H1743-322, M82~X-1, and Sgr~A$^{*}$) are used to constrain the black hole parameters through Bayesian inference and Markov Chain Monte Carlo (MCMC) analyses. For the X-ray binaries GRO J1655-40, GRS 1915+105, H1743-322, and M82~X-1, nonzero values of the dimensionless parameter $b=Bm$ are obtained at the $68\%$ confidence level within the framework of the parametric resonance model, while only upper bounds at the $90\%$ confidence level are obtained for the remaining sources. In contrast, in the case of the forced resonance model, only an upper bound at the $90\%$ confidence interval is obtained for the magnetic field parameter for all considered X-ray binary sources. The analysis indicates that the value of the magnetic field parameter is small but not negligible, producing minor modifications to particle dynamics and epicyclic frequencies. The influence of the magnetic field is further examined through the properties of the innermost stable circular orbit and the radiative properties of the thin accretion disk, including the energy flux and temperature profiles, within the allowed parameter range inferred from the MCMC analysis.
Energy extraction from a rotating Buchdahl star via magnetic reconnection
Ikhtiyor Eshtursunov, Sanjar Shaymatov
Published: 2026-03-18
Categories: gr-qc
In this work, we investigate the magnetic reconnection (MR) process as a mechanism for energy extraction from a rapidly rotating Buchdahl star (BS), one of the most compact horizonless objects that can, in principle, possess a spin parameter exceeding the extremal limit of a black hole (BH). We explore the energetics of the BS by focusing on the newly proposed MR mechanism developed by Comisso and Asenjo (the Comisso-Asenjo mechanism). Within this framework, we evaluate the energy extraction efficiency and the associated power output from a rapidly rotating BS. We show that the ergoregion of the BS exists only when the spin parameter satisfies $β>1/\sqrt{2}$. Consequently, the extraction of rotational energy through MR becomes possible only under this condition. Furthermore, we analyze the rate of energy extraction driven by fast magnetic reconnection and compare the resulting power with that predicted by the Blandford-Znajek mechanism. Our results indicate that the energy extraction rate increases significantly when the BS spin parameter exceeds the extremal limit for a BH, highlighting that MR can be substantially more efficient than the Blandford-Znajek mechanism. We demonstrate that MR can greatly enhance energy extraction efficiency from rapidly rotating BS with a large spin, making such an object potentially more efficient engines of high-energy astrophysical processes than BH.
Non-linear instability of the Kerr Cauchy horizon near $i_+$
Sebastian Gurriaran
Published: 2026-03-18
Categories: gr-qc
We consider solutions of the Einstein vacuum equations which arise from smooth initial data on a hypersurface slightly inside a dynamical black hole settling down to a subextremal Kerr black hole, and satisfying a precise non-linear Price's law-type estimate (which we expect to hold generically). We prove that the corresponding maximal globally hyperbolic development admits a non-trivial piece of future null boundary - the Cauchy horizon - emanating from timelike infinity $i_+$, which exhibits a kind of curvature blow-up, and across which the spacetime metric is Lipschitz-inextendible. Our results thus imply a Lipschitz version of Strong Cosmic Censorship for Kerr spacetimes near timelike infinity under this Price's law-type assumption. The analysis relies on the proof of the $C^0$ stability of the Kerr Cauchy horizon by Dafermos and Luk, on the non-integrable formalism of Giorgi-Klainerman-Szeftel and principal temporal gauge of Klainerman and Szeftel used in the proof of the exterior stability of slowly rotating Kerr black holes, on the linearized analysis for the Teukolsky equation inside subextremal Kerr black holes by the author, and on Sbierski's criterion for Lipschitz inextendibility. More precisely, we proceed by decomposing the black hole interior into different regions equipped with appropriate gauges, allowing for a proof of stability estimates and a thorough analysis of the non-linear analog of the Teukolsky equation, from which we infer our instability results.
Inflation with the Gauss-Bonnet term in the Palatini formulation
Ali Hassan, Syksy Rasanen
Published: 2026-03-18
Categories: astro-ph.CO
We consider the Gauss-Bonnet term coupled to the inflaton in the Palatini formulation of gravity. Unlike in the metric formulation, the Gauss-Bonnet term is not always a total derivative. We solve for the connection and insert it into the action, exactly for the spatially flat FLRW spacetime, and using the gradient approximation and order reduction for a general spacetime. We consider three cases: when the connection is unconstrained, and when non-metricity or torsion is put to zero. In all cases, the leading order change to the inflaton kinetic has the same form as that generated by the Chern-Simons term, but a negative sign. The modification of the gravitational wave sector also has the same form as in the Chern-Simons case but with a negative sign, except possibly for zero torsion, depending on the coupling and the potential. Within the range of validity of our approximations, differences from the metric formulation are small unless the kinetic term flips sign or is close to doing so.
Electromagnetic radiation-reaction near black holes: orbital widening and the role of the tail
Bakhtinur Juraev, Arman Tursunov, Zdeněk Stuchlík, Martin Kološ, Dmitri V. Gal'tsov
Published: 2026-03-18
Categories: gr-qc
We investigate the orbital evolution of a classical charged particle around a Schwarzschild black hole immersed in an external, uniform magnetic field, taking into full account both local radiation-reaction and the nonlocal tail self-force arising in curved spacetime. Starting from the DeWitt-Brehme equation and its Landau-Lifshitz reduction, we derive analytic expressions for the conservative and dissipative components of the electromagnetic self-force in both the weak-field (Newtonian) and strong-field regimes. By implementing backward-in-time integration of the third-order DeWitt-Brehme equation alongside the second-order Landau-Lifshitz equation, we demonstrate that the so-called orbital widening effect persists even when the tail term is included, and that for astrophysically realistic charge-to-mass ratios the tail contribution to the trajectory is negligible. We further show that this widening is directly controlled by the product of the magnetic field and radiation-reaction parameters and can be captured in the Newtonian limit. Finally, we identify a scaling symmetry showing that simulations with moderate parameter values can accurately represent the dynamics in realistic astrophysical conditions, confirming that orbital widening is a robust phenomenon that can persist even in astrophysical black hole environments.
Multiway junction conditions: Jackiw-Teitelboim gravity
Jia-Yin Shen
Published: 2026-03-18
Categories: hep-th
A booklet is a geometric structure formed by gluing multiple bulk spacetimes along a common interface and imposing gravitational consistency conditions at the junction. We have systematically investigated the properties of booklet structures, constructed the booklet geometry, and derived the multiway junction conditions applicable at the interface. In this work, we provide a complete solution to the multiway junction conditions for booklets composed of bulks governed by JT gravity. By constructing invariants of the dilaton solution space, we classify all dilaton configurations into three inequivalent types, each exhibiting attractive, repulsive, or neutral behavior. Through continuous isometric transformations, each type is fixed to a standard form characterized by a single physical parameter, effectively eliminating redundant degrees of freedom. This process selects a distinguished class of Poincaré coordinates for each type. Expanding the constraint equations order by order breaks coordinate invariance beyond the leading and subleading orders. By jointly solving the junction and continuity conditions up to subleading order, we find that junctions are only allowed when a sufficient number of bulks carry attractive dilatons, as captured quantitatively by a equilibrium condition. We further analyze all possible combinations of different dilaton types and determine the shape of the interface along with the explicit form of the dilaton defined on it.
Tetrads in SU(N) Yang-Mills geometrodynamics
Alcides Garat
Published: 2026-03-18
Categories: gr-qc
The discovery of the SU(3) symmetry was fundamental as to establishing an ordering principle in particle physics. We already studied how to couple the SU(3) symmetry to the gravitational field in four-dimensional curved Lorentzian spacetimes. The multiplets of equal quantum numbers are translated through natural elements in Riemannian geometry into local multiplets of equal gravitational field. As quark physics developed since the seventies, it was necessary to incorporate new symmetries to the models, that ensued in the incorporation of new quantum numbers like Charm, for example. Charm is an additive quantum number like isospin T3 and hypercharge Y and the standard T3-Y diagrams were extended onto another third axis. Then, instead of the fundamental triplet we have a quartet {u; d; s; c} as the smallest representation of the symmetry group, leading to the introduction of SU(4) as the new group of symmetries. In this paper we will not restrict ourselves exclusively to the symmetry group SU(4) and we will set out to analyze the coupling of the SU(N) symmetry to the gravitational field. To this end new tetrads will be introduced as we did for the SU(3) x SU(2) x U(1) case. These tetrads have outstanding properties that enable these constructions. New theorems will be proved regarding the isomorphic nature of these local symmetry gauge groups and tensor products of groups of local tetrad transformations. This is a paper about grand field uni?fication in four-dimensional curved Lorentzian spacetimes.
Non-Schwarzschild black holes sourced by scalar-vector fields
Manuel Gonzalez-Espinoza, Y. Gómez-Leyton, Z. Stuchlik, Francisco Tello-Ortiz
Published: 2026-03-18
Categories: gr-qc
In a scalar-vector-gravity theory with the vector sector described by nonlinear electrodynamics, the field equations are integrated using the well-known gravitational decoupling method. The resulting spacetime corresponds to a spherically symmetric and static non-Schwarzschild black hole. Employing the master equations for both even and odd parity modes, it is proven that the solution is stable under certain conditions satisfied by the scalar and vector field parameters. To further corroborate the theoretical feasibility of this toy model, the causal structure, geodesic motion for massive particles, and some thermodynamic features are analyzed in detail.
Modified Friedmann equations and non-singular cosmologies in $d=4$ non-polynomial quasi-topological gravities
Johanna Borissova, João Magueijo
Published: 2026-03-18
Categories: gr-qc
Quasi-topological theories of gravity are known to resolve black-hole singularities. We investigate whether the same mechanism can remove cosmological singularities. Focusing on non-polynomial curvature quasi-topological gravities in $d=4$ dimensions, we find three generic scenarios with the correct infrared limit but without a Big-Bang singularity, for universes filled with pure radiation or other standard matter. The first scenario yields a universe emerging from a de Sitter phase, a case for which the curvature invariants remain finite but the matter density diverges, albeit only at infinite affine distance. The second one corresponds to a bouncing universe, which requires a multi-valued Lagrangian. The third possibility is an asymptotically Minkowski origin, reminiscent of an eternally loitering universe. The matter energy density for this solution is non-singular even at infinite affine distance and does not enter a super-Planckian regime, but is instead approximately constant for the past eternity.
Scattering of a scalar field in the four-dimensional quasi-topological gravity
Alexey Dubinsky
Published: 2026-03-18
Categories: gr-qc
We study grey-body factors for a massless scalar field in the spacetime of regular black holes arising in four-dimensional non-polynomial quasi-topological gravity. We consider two representative metrics that capture the typical features of regular geometries. Using the WKB method, we compute the transmission probabilities and analyze their dependence on the regularization parameter. The grey-body factors are found to deviate only slightly from the Schwarzschild case, indicating that the scattering properties are largely insensitive to near-horizon regularization of the geometry. The correspondence between quasinormal modes and grey-body factors is shown to be sufficiently accurate for higher multipole numbers.
On the concept of simultaneity in relativity
Justo Pastor Lambare
Published: 2026-03-18
Categories: gr-qc
In this comment, we demonstrate that the claim by Spavieri et al., asserting that Wang et al.'s interferometric experiment disproves the special theory of relativity by revealing that simultaneity must be an absolute concept independent of the observer's state of motion, is based on circular reasoning and therefore constitutes a logical fallacy.
Forecasting Sensitivity to Modified Dispersion Effects in Pulsar Timing Arrays
Jonathan Grée, Qiuyue Liang, Elisa G. M. Ferreira
Published: 2026-03-18
Categories: astro-ph.CO
The pulsar timing array systems have reported a detection of a nanohertz-band stochastic gravitational wave background in our galaxy. It is of interest to use this observation to probe modified gravity and to forecast the sensitivity with which certain deviations can be tested in the coming years. In this paper, we focus on the modified dispersion relation of the tensor modes and its effect on the overlap reduction function of the timing residual cross-correlations. We perform a comprehensive forecast of the phase velocity uncertainty, $σ_v$, using a Fisher analysis validated by a mock-data study to account for potential non-Gaussian behavior. We also take into account the sample variance effect and provide an observational timeline for future PTA sensitivity: detecting a $10\%$ or $-1\%$ deviation from the speed of light at the $3σ$ level requires $\mathcal{O}(30)$ years of observations.
Tightening Cosmological Constraints Within and Beyond $Λ$CDM Using Gamma-Ray Bursts Calibrated with Type Ia Supernovae
Wei Hong, Luca Izzo, Massimo Della Valle, Orlando Luongo, Marco Muccino, Tong-Jie Zhang
Published: 2026-03-18
Categories: astro-ph.CO
Context. Gamma-ray bursts (GRBs) reach redshifts beyond Type Ia supernovae (SNe Ia) and can extend distance measurements into the early Universe, but their use as distance indicators is limited by the circularity problem in calibrating empirical luminosity relations. Aims. We present a model-independent methodology to overcome this circularity by combining Pantheon$+$ SNe Ia, a distance reconstruction based on artificial neural networks (ANNs), and two GRB correlations (Amati and Combo) into a distance ladder from low to high redshift, with the goal of constraining cosmological parameters in $Λ\mathrm{CDM}$ and $w_0 w_a \mathrm{CDM}$. Methods. We use the ReFANN to reconstruct the luminosity distance $d_L(z)$ and distance modulus $μ(z)$ from the Pantheon$+$ dataset, with hyperparameters optimized via approximate Bayesian computation rejection and a risk function. This model-independent reconstruction calibrates the Amati and Combo relations using a low-redshift ($z<1$) GRB sample from Fermi GBM and Swift-XRT. The calibrated relations then provide distance estimates for GRBs at $z \geq 1$. Finally, a joint Bayesian analysis simultaneously constrains the cosmological and GRB correlation parameters, ensuring self-consistent uncertainty propagation. Results. We obtain consistent cosmological constraints from two independent GRB correlations. The Hubble constant $H_0$ agrees with SNe Ia values, though potentially influenced by Pantheon$+$ dataset. High-redshift GRBs favour a higher matter density $Ω_m$ than the Pantheon$+$ and hint at possible dark energy evolution.Conclusions. We present a framework that mitigates GRB cosmology's circularity problem, extending the distance ladder to $z \sim 9$ and establishing GRBs as a high-redshift probe.
Natura Non Facit Saltum: An Analytical Model of Smooth Slow-Roll to Ultra-Slow-Roll Transition
Diego Cruces, Minxi He, Shi Pi, Jianing Wang, Masahide Yamaguchi, Yuhang Zhu
Published: 2026-03-18
Categories: astro-ph.CO
In this letter, we propose a single-field inflation model that realizes a slow-roll-to-ultra-slow-roll transition while keeping the second slow-roll parameter smoothly varying throughout. The model is built through a minimal modification by introducing a simple time dependence in the effective mass term of the Mukhanov-Sasaki equation. We obtain fully analytical solutions for both the background evolution and the curvature perturbations, which makes the parameter dependence of the curvature power spectrum easy to track. To the best of our knowledge, this is the first analytical model that describes a smooth transition of this kind. We also compare its signatures with those of the corresponding sharp-transition counterpart.
Fluxes of Generic Extreme-Mass-Ratio Inspirals with a Spinning Secondary
Qiuxin Cui, Wen-Biao Han
Published: 2026-03-18
Categories: astro-ph.HE
Extreme mass-ratio inspirals (EMRIs), comprising a stellar-mass compact object (CO) orbiting a supermassive black hole (BH), are key targets for future space-based gravitational-wave (GW) observatories. Incorporating the spin of the secondary body into waveform models not only enhances measurement precision but also offers insight into the spin distribution of stellar-mass objects. In this work, we construct the flux and waveform for an EMRI with a spinning secondary in a Kerr background under the linear-spin approximation. Using the radiative prescription (half-retarded minus half-advanced field), we derive orbit-averaged evolution equations for the fundamental constants of motion, including the energy, angular momentum, Carter-like constant, and the parallel spin component. This framework provides a tractable route to generating waveforms that incorporate the secondary spin, with the potential for further simplification in future work.
More on near-horizon charges black holes with gravitational hair in three dimensions
Seyed Naseh Sajadi, Supakchai Ponglertsakul, Julio Oliva
Published: 2026-03-18
Categories: gr-qc
With the aim of continuing the exploration of near-horizon charges in higher-curvature gravity, searching for sectors leading to universal behaviors, we first provide a thorough revision and formulae of the covariant phase-space method applied to arbitrary gravitational theories containing up to quartic terms in the Riemann tensor in arbitrary dimension. These results can be applied in diverse setups, in particular in the context of $α'$ corrections to String Theory, where it is known that in Type II theories, the first correction to the Einstein-Hilbert Lagrangian goes as $α'^3 \mathcal{R}^4$. Then, we test these formulae for near horizon asymptotic symmetries of the rotating BTZ spacetime where the first law of black hole thermodynamics is consistently recovered. It was recently realized that a subset of these higher curvature gravities do admit black holes with gravitational hair, whose entropy can be microscopically accounted for, as is the case of New Massive Gravity. In this case, the four maximally symmetric vacua of the theory coincide, and the theory acquires an extra gauge symmetry when linearized around such a vacuum. We study the near-horizon asymptotic symmetries and compute the associated charges, both in the static and rotating hairy black holes, extending up to $\mathcal{R}^4$, a work that was previously done only up to a quadratic term. In order to allow for a continuous lecture on the work, we report the explicit expressions of the general Lagrangians in the appendices.
When do real observers resolve de Sitter's imaginary problem?
Ahmed Farag Ali
Published: 2026-03-18
Categories: hep-th
The universal phase $\rev{\ii}^{D+2}$ of the Euclidean de Sitter path integral obstructs a straightforward state-counting interpretation of the Gibbons--Hawking entropy. Building on Maldacena's proposal that specific black-hole observers can reorganize this phase, we derive a general constraint on when such ``real observers'' can succeed. By distinguishing \emph{gravitational observers} from \emph{topological spectators}, we show that any sector whose \emph{infrared effective} action is metric independent at the de Sitter saddle factorizes in the path integral, $\Ztot = \Zgrav^{(\text{obs})}\Ztop$, so the imaginary phase persists regardless of the sector's information-processing capabilities. Using confining $\SU(3)$ gauge theory and topological orders as examples, we demonstrate that an information-bearing clock is necessary but insufficient: only observers whose fluctuations share the negative modes of the conformal factor belong to the special class that can remove the de Sitter phase.
Kalb-Ramond Topological Term in Majorana Superspace and Kaluza-Klein Spectrum Deformation in Five Dimensions
L. A. S. Nunes, C. A. S. Almeida
Published: 2026-03-18
Categories: hep-th
We construct the supersymmetric extension of the Kalb-Ramond topological term in an intrinsic $N=1$, $D=5$ superspace based on Majorana spinor coordinates. This formalism is a Majorana-basis implementation of the $N$=$1/2$ superspace of Linch, Luty and Phillips, and is particularly well suited to theories with torsion: the Majorana condition is the natural spinor structure in five dimensions, orbifold parity acts directly at the level of the Grassmann coordinate, and bulk matter couplings to the Kalb--Ramond field require no intermediate change of spinor basis. The covariant derivatives of the formalism carry an explicit dependence on the fifth-coordinate derivative, absent in the pseudo-supersymmetric approach of Klein. This generates two new contributions to the component action - one bosonic, one fermionic - that are invisible in any treatment based on four-dimensional superspace derivatives. We further show that the fermionic partner of the bosonic topological term is itself a topological structure, so that the supersymmetric extension preserves the background-independence of the original theory. The identification of the mixed Kalb-Ramond component with a gauge vector, implemented at the superfield level, yields a fully supersymmetric Chern-Simons-like coupling for the first time in this framework. Upon compactification, the new bosonic term shifts the entire Kaluza-Klein mass spectrum of the Kalb-Ramond tower by a factor proportional to the topological coupling constant - a concrete prediction absent in both the purely bosonic and pseudo-supersymmetric treatments, with direct implications for torsion phenomenology in Randall-Sundrum brane-world models.
The EPRL amplitude is supported on flat connections
Carlos E. Beltrán, José A. Zapata
Published: 2026-03-17
Categories: gr-qc
For the version of the EPRL model based on the original vertex amplitude and the face amplitude selected by its gluing properties, we prove that the EPRL amplitude of any region with the topology of a 4-ball is supported on flat connections. We state immediate consequences of this result, comment on some applications, and discuss physical implications. The results hold in general; they do not rely on a semiclassical analysis.
Quantifying the Scientific Potential of Intermediate and Extreme Mass Ratio Inspirals with the Laser Interferometer Space Antenna
Lorenzo Speri, Francisco Duque, Susanna Barsanti, Alessandro Santini, Shubham Kejriwal, Ollie Burke, Christian E. A. Chapman-Bird
Published: 2026-03-17
Categories: astro-ph.IM
The Laser Interferometer Space Antenna (LISA) will enable precision studies of Extreme and Intermediate Mass Ratio Inspirals (EMRIs/IMRIs), providing unique probes of astrophysical environments of galactic nuclei and strong-field gravity. Using a fully relativistic pipeline across primary masses $m_1 \in [5\times10^4, 10^7]\,M_\odot$ and secondary masses $m_2 \in [1, 10^4]\,M_\odot$, we map instrumental performance directly to detection horizons and parameter measurement precision. EMRIs with $m_1 = 10^7\,M_\odot$ and $m_2 \sim 1\,M_\odot$ are the most sensitive to instrument degradation, with redshift horizons at $z \sim 0.01$, while IMRIs are the least sensitive to degradation and reach redshifts $z \sim 1-3$. All prograde systems considered achieve sub-percent spin precision within three months of observation. The full 4.5-year mission increases the horizon of systems with $m_1 = 10^7\,M_\odot$ and $m_2 \sim 1\,M_\odot$ by a factor of $\sim 4$ and improves sky localization by one to two orders of magnitude reaching $ < 10\,\mathrm{deg}^2$. IMRI detection is robust against degradation, but their parameter estimation is more vulnerable due to fewer cycles in band. With the full baseline, EMRI observations constrain scalar dipole emission and Kerr quadrupole deviations below ground-based bounds by one to two orders of magnitude. We release the accompanying software and an interactive website to enable the community to rapidly quantify the scientific potential of EMRIs and IMRIs.
False vacuum decay catalyzed by black hole in a heat bath
Bowen Hu, Kohei Kamada, Andrey Shkerin
Published: 2026-03-17
Categories: hep-th
We study false vacuum decay catalyzed by black holes. We consider a scalar field model with unstable potential in the background of a dilaton black hole in two dimensions. The model reproduces many features of the Schwarzschild black hole background in four dimensions, including the centrifugal barrier for linearized field perturbations. We study decays from the non-equilibrium state describing the evaporating black hole immersed in the thermal bath with a different temperature. We analytically construct the tunneling solution relevant at small field excitations and evaluate the decay suppression. We show how they reduce to those for the Hartle-Hawking (equilibrium) and Unruh states in the corresponding limits. For large field excitations the decay proceeds via stochastic activation; we find the relevant non-thermal sphaleron configuration in a certain region of parameters of the model and construct the semiclassical solution describing tunneling onto this sphaleron. Our results provide insights into the vacuum decay induced by small primordial black holes in the radiation-dominated era of the universe.
The two shadows of a single black hole: Vacuum birefringence phenomena within Einstein-Nonlinear-Electrodynamics
Marco A. A. de Paula, Haroldo C. D. Lima, Pedro V. P. Cunha, Carlos A. R. Herdeiro, Luís C. B. Crispino
Published: 2026-03-17
Categories: gr-qc
One of the main features of nonlinear electrodynamics (NED) is the existence of an effective geometry that describes the geodesic motion of photons. A detailed analysis of the properties of effective geometry is of utmost importance for a better understanding of NED theories and their possible imprints on physics, especially in the context of black holes (BHs). We consider a NED model that depends on the two electromagnetic scalar invariants and obtain that the motion of photons in NED exhibits \textit{vacuum birefringence}, i.e., photons can propagate along two distinct paths, depending on their polarization. As a consequence of this phenomenon, we show that static black hole solutions sourced by NED can admit two distinct unstable light rings, leading to the formation of two distinct shadows. Moreover, to explore the potential astrophysical relevance of our results, we also compare them with the astrophysical observations for the shadow radius of Sagittarius A*. We place upper limits on the charge-to-mass ratio of the NED-sourced black hole. We also show that the motion of photons in this context can be interpreted as nongeodesic curves subjected to a four-force term from the perspective of an observer in the spacetime metric, generalizing previous results in the literature for NED models that depend on a single electromagnetic scalar invariant.
What Shape is the Inflationary Bispectrum?
Oliver H. E. Philcox
Published: 2026-03-17
Categories: astro-ph.CO
Non-linear interactions during inflation generate non-Gaussianities in the distribution of primordial curvature. In many theories, the physics is scale-invariant, such that the induced three-point function depends solely on a dimensionless shape function $S(x,y)\sim k^6B_ζ(kx,ky,k)$. To confront such models with observations, one typically builds specialized estimators for each shape, then applies them to cosmic microwave background datasets at significant computational expense. In this Letter, we take a different approach, directly reconstructing $S(x,y)$ from observations using an efficient logarithmically-binned estimator in primordial-space (motivated by the modal program). Applying this to temperature and polarization maps from Planck, we obtain high-resolution shape measurements across the full $(x,y)$-plane, including squeezed limits. Our approach is close-to-optimal, highly interpretable, and preserves the information content on (optimally-analyzed) standard templates within $\approx 10\%$; moreover, we can use it to assess the scale-dependence of our constraints, finding that Planck is sensitive to $\approx 6$ $e$-folds of non-Gaussian evolution with a peak sensitivity around $0.1h\,\mathrm{Mpc}^{-1}$. Since we work directly in shape-space, data and theory can be compared in milliseconds. As an example, we perform a search for massive particle exchange using a suite of over $20\,000$ theoretical templates computed with exact bootstrap methods (for the first time) across a wide range of masses, spins, and sound-speeds; the spin-two analysis yields a maximum significance of $2.6σ$. Our approach can be used to probe a wide range of scale-invariant models in orders-of-magnitude less time than with direct estimators, allowing the inflationary paradigm to be explored in new ways.
The Structure of the Continuum Limit of Spin Foams
Matteo Bruno, Eugenia Colafranceschi, Fabio M. Mele, Carlo Rovelli
Published: 2026-03-17
Categories: gr-qc
The Spin Foam approach to quantum gravity aims at providing a covariant path-integral formulation of canonical Loop Quantum Gravity. Since spin foam amplitudes are defined through discretisations of spacetime, understanding the continuum limit of the theory remains a central open problem. In this work, we investigate the structural aspects of this limit in a model-independent manner. We begin by introducing an axiomatic framework for spin foam amplitudes inspired by Atiyah's formulation of Topological Quantum Field Theories (TQFTs). In this setting, Hilbert spaces and amplitudes are assigned to combinatorial and topological data associated with triangulated manifolds. By equipping the set of triangulations with suitable orders, this framework provides a precise notion of continuum limit and allows us to analyse its properties independently of any specific model. We proceed then to systematically investigate how the specifics of the limit procedure allow to go beyond TQFT in the continuum. Under natural assumptions on the convergence of spin foam amplitudes, we establish a no-go result: sufficiently strong notions of convergence necessarily lead to a topological theory. Motivated by this obstruction, we weaken the notion of convergence and consider the continuum limit of spin foam amplitudes in a distributional sense, in the spirit of Refined Algebraic Quantisation. Under this assumption, the amplitude associated with the cylinder defines a rigging map, yielding a canonical construction of the physical Hilbert space. The resulting continuum amplitudes act as well-defined distributions on this space of physical states, characterising this formulation of the gravitational path integral as physical in a precise sense.
The imitation game (r)evolutions: $Q$-star effective shadow from GRMHD analysis
Víctor Jaramillo, Laura Meneses, Héctor R. Olivares Sánchez, Carlos Herdeiro, Darío Núñez, Shuang-Yong Zhou
Published: 2026-03-17
Categories: gr-qc
$Q$-stars are a class of boson stars arising in scalar-field theories with interacting potentials, minimally coupled to gravity. We show that, in certain regions of parameter space, the angular velocity of stable timelike circular geodesics around $Q$-stars can attain a maximum at a nonzero radius. Notably, this behaviour may occur for stable configurations. This feature has been argued to produce effective shadows, but so far it has only been investigated for unstable solutions. We test this possibility by performing general relativistic magnetohydrodynamic evolutions for a representative stable $Q$-star model. A low-density, low-luminosity central region is indeed observed to form and persist -- at least until the evolution becomes affected by numerical viscosity. As a proof of principle, this suggests that families of stable bosonic stars can act as black hole mimickers. Moreover, for the model at hand, a heuristic analysis shows that the effective shadow has a comparable size to that of a Schwarzschild black hole with the same mass. Importantly, this mechanism for generating an effective shadow does not rely on the object being ultracompact, or an ad hoc chosen accretion disk.
Beyond $Λ$CDM with a Logistic RG-like Flow of the Low Redshift Cosmic Evolution
Shibendu Gupta Choudhury, Anjan A Sen
Published: 2026-03-17
Categories: astro-ph.CO
Recent cosmological observations show hints for possible deviations from the standard $Λ$CDM paradigm at late times. To study such deviation, we introduce a minimal phenomenological framework in which the total equation of state of the Universe, $w_{\rm T}(z)$, follows a logistic evolution motivated by a renormalization group like flow between cosmological fixed points. This approach directly reconstructs $w_{\rm T}(z)$ probed by background observables, without assuming a specific dark energy model. Using DESI-DR2 baryon acoustic oscillation measurements, DES-Dovekie latest supernova data, and CMB distance priors, we find that the logistic parametrization provides an improved fit compared to $Λ$CDM and remains competitive with standard dynamical dark energy models. The inferred expansion history exhibits noticeable deviations from $Λ$CDM at low redshifts, reflected in the reconstructed jerk parameter. While the statistical significance of these deviations is model-dependent, our results highlight the potential of flow-inspired parametrizations as a complementary and physically interpretable framework for probing late-time cosmic dynamics.
Solving gravitational field equations by Wiener-Hopf matrix factorisation, and beyond
M. Cristina Câmara, Gabriel Lopes Cardoso
Published: 2026-03-17
Categories: math-ph
By viewing Einstein's field equations -- reduced to two dimensions -- as an integrable system, one can simultaneously obtain exact solutions to both the equations themselves and their associated Lax pair via a canonical Wiener-Hopf factorisation of a so-called monodromy matrix. In this article, we review this remarkable interplay between gravitational field equations, integrable systems, Riemann-Hilbert problems, and Wiener-Hopf factorisation theory, with particular emphasis on developments from the past decade enabled by advances in Wiener-Hopf factorisation techniques arising from the study of singular integral equations and Toeplitz operators. Through a variety of concrete examples, we illustrate how Wiener-Hopf factorisation yields explicit, exact solutions to the field equations of gravitational theories, and how its generalisation through a so-called $τ$-invariance property provides a new solution-generating method. Along the way, we aim to demonstrate the importance of an interdisciplinary approach -- grounded in General Relativity, Complex Analysis, and Operator Theory -- for the study of gravitational field equations.
Measurement-Based Estimation of Causal Conditional Variances and Its Application to Macroscopic quantum phenomenon
Kosei Hatakeyama, Ryotaro Fukuzumi, Akira Matsumura, Daisuke Miki, Kazuhiro Yamamoto
Published: 2026-03-17
Categories: quant-ph
We analytically investigate a quantum estimation method for a mechanical oscillator in a detuned cavity system based solely on homodyne measurement records, building on the framework developed by C.Meng et al. (Science Advances 8, 7585 (2022)). Estimation based only on measurement records is important because it enables state verification without assuming knowledge of the true system state. We construct a relative estimate operator from causal and anti-causal quantum Wiener filters and calculate its variance. The deviation from the causal conditional variance is defined as a reconstruction bias, whose magnitude is evaluated analytically. We show that, within experimentally relevant parameter regimes for typical quantum-state preparation, the reconstruction bias is sufficiently small to be neglected. As applications to state verification, we apply the method to proposals for macroscopic quantum entanglement mediated by electromagnetic interactions and for conditional momentum-squeezed states generated by homodyne detection, and clarify the conditions under which the bias remains negligible and when the reconstruction bias becomes significant.
Decoherence and the Reemergence of Coherence From a Superconducting "Horizon"
Eric J. Sung, Charles A. Stafford
Published: 2026-03-17
Categories: quant-ph
In a recent paper arXiv:2205.06279, Danielson et al. demonstrated that the mere presence of a black hole causes universal decoherence of quantum superpositions (dubbed the DSW decoherence). This result has profound implications for the interplay of quantum mechanics and gravity. We analyze decoherence in a superconducting analogue arXiv:1709.06154 of the event horizon of a black hole, where Andreev reflection plays the role of Hawking radiation. We consider a normal metal interferometer threaded by an Aharonov-Bohm flux, where one of the arms of the interferometer is coupled to a superconductor by a tunnel coupling of varying strength. At absolute zero and for weak coupling, we find that the scattering states of the interferometer are decohered by Andreev reflection, a nontrivial manifestation of the proximity effect analogous to DSW decoherence from the event horizon of a black hole. However, for increasing coupling strength to the superconductor, we find a reemergence of coherence via resonant tunneling through Andreev bound states. This suggests the existence of an analogue gravitational phenomenon wherein transmission mediated by virtual Hawking radiation leads to a reemergence of coherence in an interferometer placed within a few Compton wavelengths of a black hole's event horizon. Our results open a new path to study black hole quantum physics on earth via analogue studies.
Curvature inequalities and rigidity for constant mean curvature and spacetime constant mean curvature surfaces
Alejandro Peñuela Diaz
Published: 2026-03-17
Categories: math.DG
We establish curvature inequalities and rigidity results for surfaces satisfying constant mean curvature type conditions in both Riemannian and Lorentzian geometry. In the Riemannian setting we study constant mean curvature (CMC) surfaces in three-dimensional manifolds with scalar curvature bounds. Building on the Christodoulou-Yau inequality $H^2\leq 16π/ |Σ|$ (with $H$ the mean curvature and $|Σ|$ the area), we show that the associated rigidity phenomena persist under a weaker notion of stability controlling only the constant mode of the second variation, combined with an extrinsic curvature sign condition. This yields Euclidean rigidity without imposing intrinsic symmetry or near-roundness assumptions and extends to higher dimensions and to the hyperbolic and spherical settings. In the Lorentzian setting we consider spacetime constant mean curvature (STCMC) surfaces, a natural generalization of CMC surfaces. We introduce a stability theory for STCMC surfaces and prove the sharp inequality $|\vec{H}|^2\leq 16π/ |Σ|$ under the dominant energy condition. We also obtain rigidity for the equality case: under suitable geometric assumptions the surface is intrinsically round and the spacetime region it bounds is flat, with maximal globally hyperbolic development isometric to a causal diamond in Minkowski spacetime. Finally, we show that the canonical asymptotic STCMC foliations known in both the spacelike and null settings have leaves that are stable with respect to this notion of stability.
Dyonic Einstein-Maxwell-scalar black holes: the cold, the hot and the plunge
Shun Chen, Xiao Yan Chew, Jutta Kunz
Published: 2026-03-17
Categories: gr-qc
We investigate dyonic nonlinearly scalarized black holes in Einstein-Maxwell-scalar theory. The domain of existence of scalarized dyonic black holes consists of three branches. The cold branch and the hot branch bifurcate at a minimal value of the charge, analogous to the purely electrically charged scalarized black holes. However, the presence of both charges allows for regular extremal black holes, leading to a third branch featuring a sudden plunge in Hawking temperature. In fact, the presence of both electromagnetic charges introduces a factor $Δ(φ)$ in the source term of scalar field equations that vanishes when the coupling function $f(φ)$ equals the ratio of the charges for some value of the scalar field $φ_c$. The scalar field of extremal black holes assumes precisely this value at the horizon, $φ_H=φ_c$. We demonstrate the plunge for the coupling function $f(φ)=\exp(αφ^3)$.
Testing general relativity with binary black holes: a study on the sensitivity requirements for future space-based detectors
Tangchao Zhan, Changfu Shi, Shuo Sun, Jianwei Mei
Published: 2026-03-17
Categories: gr-qc
We study the sensitivity required for a future space-based detector to search for beyond general relativity effect in gravitational wave detection. To do this, we use the current design of TianQin, LISA, and $μ$Ares as starting points, and study how their key noise parameters should be improved to adequately detect some target signals, for which we choose a nonlinear ringdown mode, displacement memory, and a putative beyond general relativity signal, all from the merger of massive black hole binaries. We find that the required improvements are strongly dependent on the choice of the target signals and the population model of massive black hole binaries, and $4-9$ orders of magnitude improvement will be needed in the most demanding detection scenarios.
Energy Conditions in Gauss-Bonnet Gravity
Francesco Bajardi
Published: 2026-03-17
Categories: gr-qc
We study the Energy Conditions in modified $f(G)$ gravity, with $G$ being the topological Gauss-Bonnet term. Then we use the cosmographic parameters to constrain the functional form of the gravitational action and investigate the possibility to have standard inflation in the early time. Specifically, we select models containing symmetries within the modified $f(\G)$ theory and obtain conditions for which i) the energy conditions can be violated and ii) the magnitude of the slow-roll parameters is small, thus suggesting that under given limits the analyzed theory can potentially trace the cosmic history both at early and at the late times.
Hawking-Page phase transitions of black holes in the Hamiltonian formalism
Tran Ngoc Thien, Vo Quoc Phong
Published: 2026-03-17
Categories: gr-qc
The Hawking-Page phase transition represents a critical phenomenon in black hole thermodynamics, marking the point at which a thermal radiation state in anti-de Sitter (AdS) spacetime becomes unstable. In this work, we apply the Hamiltonian formalism to study the Hawking-Page phase transition of the Banados-Teitelboim-Zenelli (BTZ) black hole in on-shell and off-shell configuration. The results show that the Hamiltonian of the black hole system corresponds to its thermodynamic free energy. Next, we examine the Hawking-Page phase transition of the Reissner-Nordstrom (RN) black hole and the Kerr-Newmann (KN) black hole, and compare our results with existing results in on-shell case. We then further extend this method to the previously unexplored off-shell case of the RN and KN black holes, thereby demonstrating the influence of the electric charge and the rotation of the black hole on their Hawking-Page phase transition. The results show that, in the presence of electric charge and totation, enables the coexistence of black hole and the thermal soliton states.
Extended Theories of Electrodynamics in $f(R)$ Gravity
Francesco Bajardi, Micol Benetti, Salvatore Capozziello, Abedennour Dib
Published: 2026-03-17
Categories: gr-qc
Within the general framework of $f(R)$ gravity, we introduce a function of the electromagnetic curvature invariant $f(\mathbb{F})$ that couples minimally to gravitation to ensure a consistent treatment of curvature functions in these theories. We show that one of the solutions leads to field equations that are a generalization of the Klein-Gordon equation while the other leads to a typically non-linear massless solution. Focusing on flat spacetime, our formalism recovers the Plebanski family of models and Bopp-Podolsky electrodynamics as specific limits. These extensions may have phenomenological consequences in extreme environments, such as the early universe or near charged compact objects, where deviations from classical electrodynamics might be probed.
Testing the Coexistence of Dark Energy and Dark Matter with Late-time Observational Data
Shambel Sahlu, Andronikos Paliathanasis, Genly Leon, Amare Abebe
Published: 2026-03-17
Categories: astro-ph.CO
We investigate the viability of a cosmological scenario with interacting dark sector, which can describe the coexistence between dark energy and dark matter. The model possesses an analytical solution for the Hubble function and we constrain the free parameters by applying the newly released cosmic chronometers data (31 old data and 3 new data from DESI), the Baryonic Acoustic Oscillators from the Dark Energy Spectroscopic Instrument Survey (DESI DR2 BAO), along with Gamma-ray bursts (GRBs) and Supernova catalogues (Pantheon Plus, Union3, and DES-Dovekie). We find that the coexistence model fits the data sets in a better way than the reference models - the $Λ$CDM and $w$CDM models. The analysis shows that the coexistence scenario can provide a cosmologically viable model for the description of the late-time acceleration of the universe. Nevertheless, for large redshifts, the model has a similar behaviour to that of the $w$CDM model, as the introduction of the GRB data indicates in the statistical parameters. Finally, it is worth mentioning that the coexistence model provides a statistically smaller value for the $H_{0}$ parameter.
Gravitational Metric of a Star
Poul H. Damgaard, Hojin Lee, Kanghoon Lee, Tabasum Rahnuma
Published: 2026-03-17
Categories: hep-th
Solving the classical equations of motion in general relativity recursively, we consider the metric of a spatially localized and stationary source of matter. Having in mind a star of general composition, we characterize it by means of its infinite set of mass and current multipoles. Specializing to de Donder gauge we set up the recursive equations that produce the metric outside the star to any desired order in perturbation theory, expanded both in Newton's constant and in the order of multipoles. Up to second post-Minkowskian order we express the result to any order in the multipole expansion in terms of generalized (tensor) bubble integrals in momentum space and a corresponding simple expansion in inverse distances. In a special corner of the space of multipoles we recover the Kerr black hole solution to the given order. By tweaking just slightly the multipoles away from the Kerr limit the metric will describe stars that are Kerr-like and yet are not black holes. A subtlety with respect to the gauge ambiguity of de Donder gauge is also pointed out.
Perturbative Effects of Dark Matter Environments on Black Hole Shadows
Gabriel Gomez
Published: 2026-03-17
Categories: astro-ph.CO
Constructing spacetime solutions that describe black holes embedded in dark matter environments is a crucial step toward probing the properties of dark matter in the strong-field regime of gravity. At present, however, there is no unique or systematic framework to model such configurations, and several commonly adopted approaches raise methodological ambiguities. Motivated by these challenges, we build upon a perturbative framework to describe deformations of static, spherically symmetric black holes induced by a surrounding dark matter distribution. Within this framework, we compute the leading-order corrections to both the photon-sphere radius and the radius of the black hole shadow, assuming a generic dark matter halo profile. We then apply the formalism to physically motivated density profiles, including the Hernquist and Navarro-Frenk-White models, obtaining closed-form analytical expressions for the perturbed metric functions and for the critical impact parameter in the Schwarzschild background. Using these results, we obtain quantitative estimates for the corresponding shadow deviations and find that they lie well beyond the current observational bounds set by Keck and VLTI measurements. As a consistency check, we further estimate the total dark matter mass enclosed within the orbital radius of the S2 star and show that it remains well below the $0.1\%$ upper limit reported by the GRAVITY collaboration. Overall, this approach offers a systematic avenue to investigate perturbative effects of dark matter on black hole phenomenology, including potential implications for gravitational wave observations.
Violation of Cosmic Censorship in Einstein-Maxwell-Scalar Models with Fractional Coupling
Yan-Qing Xu, Rui-Feng Zheng, Yu-Peng Zhang, Cheng-Yong Zhang
Published: 2026-03-17
Categories: gr-qc
The weak cosmic censorship conjecture plays a foundational role in classical gravity by asserting that spacetime singularities are generically hidden behind event horizons. In this work, we explore its robustness in the Einstein-Maxwell-Scalar theory with fractional coupling by studying both static black hole solutions and their fully nonlinear dynamical evolution. We identify a class of scalarized black holes that develop negative energy density near the event horizon, indicating violations of the classical energy conditions. Numerical evolutions of perturbed configurations reveal that sufficiently strong fractional coupling drives rapid curvature growth and geometric degeneration in the near-horizon region, accompanied by persistent negative energy density. While the simulations do not resolve the ultimate end state, the observed dynamics consistently point toward a weakening of the horizon-supporting structure and are suggestive of incipient naked singularity formation. These results uncover a classical mechanism through which fractional coupling can challenge the validity of the weak cosmic censorship conjecture in asymptotically flat spacetimes.
Detectability of Nearby Binary Neutron Stars with Future sub-mHz Gravitational Wave Missions
Zhiwei Chen, Youjun Lu, Yuchao Luo, Jihui Zhang, Xiao Guo, Jifeng Liu, Wei-Tou Ni
Published: 2026-03-17
Categories: astro-ph.HE
Binary neutron stars (BNSs) are one of the most important gravitational wave (GW) sources, which provide key insights to evolution of massive binary stars and nuclear physics. Beyond Laser Interferometer Space Antenna (LISA), Taiji, and Tianqin missions, proposed concepts for next generation space-based GW observatories, including LISAmax, Folkner, and eASTROD, aim to explore the sub-millihertz (mHz) to microhertz ($μ$ Hz) frequency band. Because the proposed designs substantially suppress low-frequency noise, these detectors are expected to outperform LISA, Taiji, and Tianqin in detecting eccentric Galactic BNS systems. In this paper, we estimate the detectability of nearby inspiraling BNSs using future sub-mHz GW detectors. By utilizing compact binary population synthesis simulations to generate mock BNS samples and estimate their signal-to-noise ratios (SNRs) correspondingly for each GW detector over an observation period of $5-10$\,years, we find that LISAmax may detect $\sim 520-900$ Galactic BNSs, whereas Folkner and eASTROD may detect $\sim 780-1370$ Galactic BNSs. Notably, LISAmax excels in detecting highly eccentric systems $(e>0.90)$ owing to its higher sensitivity at relatively higher sub-mHz frequencies. We further identify seven observed radio BNSs as viable candidates for validation, in particular J0737-3039, which reaches an SNR of $\sim 100$. The expected detection number of LMC inspiraling BNSs is about $\sim 4-18$ for these sub-mHz detectors over an observation period of $5-10$\,years, while detecting inspiraling BNSs in SMC is challenging. This study highlights the significant potential of future sub-mHz GW missions in unraveling BNS formation and evolution physics.
Repetitive Penrose process in Konoplya-Zhidenko rotating non-Kerr black holes
Xiao-Xiong Zeng, Dong-Ping Su, Ke Wang
Published: 2026-03-17
Categories: gr-qc
This paper investigates the repetitive Penrose process in Konoplya-Zhidenko rotating non-Kerr black hole, exploring the influence of the deformation parameter on the repetitive Penrose process. After a brief review of the Konoplya-Zhidenko rotating non-Kerr black hole, we study the fundamental equations of the Penrose process in this spacetime, examine the iterative stopping conditions required for the repetitive Penrose process, and obtain the corresponding numerical results. It is concluded that, in addition to previously observed phenomena, under the same decay radius, a larger initial dimensionless deformation parameter $\hatη$ leads to greater values of the energy return on investment and energy utilization efficiency, particularly at higher decay radii. Furthermore, a smaller initial $\hatη$ results in a larger maximum value of the energy return on investment. For energy utilization efficiency, the initial $\hatη$ should take an intermediate value to maximize its peak. Additionally, we find that a larger initial $\hatη$ corresponds to a smaller maximum value of the extracted energy.
Ringdown bounds and spectral density limits from GWTC-3
Christian Balfagon
Published: 2026-03-17
Categories: gr-qc
We establish the first observational bounds on causal nonlocal extensions of gravity characterized by retarded Stieltjes-type kernels with positive spectral density rho(mu) >= 0, using two complementary gravitational-wave channels. From a Bayesian ringdown analysis of 17 binary black hole events in the LIGO-Virgo GWTC-3 catalogue, we set an observational ceiling on universal fractional quasi-normal mode deformations of |epsilon_Omega| < 0.05 (90% C.L.), with a cumulative log Bayes factor ln B = -0.46 +/- 0.77. By mapping published GWTC-3 modified dispersion relation bounds together with the GW170817 propagation speed constraint onto the Stieltjes spectral parameter space (mu_char, M0), we exclude a broad class of infrared-extended spectral densities with mu <= 10^{-6} m^{-2}, thereby ruling out non-trivial regions of the nonlocal kernel parameter space for the first time. The theoretically motivated fiducial range mu_char ~ M_*^2 ~ 10^8-10^10 m^{-2} satisfies all current bounds. We further show that sub-millimetre gravity experiments, which already operate at the predicted causal scale l_* ~ 10^{-4} m, provide the most promising path toward a direct test. These results define quantitative benchmarks against which future observations across the gravitational-wave, short-range gravity, and cosmological sectors can be compared.
Sensitivity of neutron star observables to microscopic nuclear parameters of realistic equations of state
Nikolas Cruz-Camacho, Carlos Conde-Ocazionez, Veronica Dexheimer, Jacquelyn Noronha-Hostler, Nicolás Yunes
Published: 2026-03-16
Categories: nucl-th
The equation of state of matter at supranuclear densities governs the astrophysical observables of neutron stars. A realistic, though complex, description is provided by the Chiral-Mean-Field model, which depends on many microscopic nuclear-physics parameters. We present a Fisher-information-inspired analysis of the sensitivity of neutron-star observables to the parameters of the Chiral-Mean-Field model at $β$-equilibrium using SLy as a crust. We then compute neutron-star sequences and extract masses, radii, compactnesses, and tidal deformabilities. From the logarithmic derivatives of these observables with respect to each nuclear parameter, we construct a dimensionless, Fisher-inspired sensitivity matrix and perform a principal-component analysis to identify the effective combinations of nuclear parameters that most strongly affect neutron-star observables. Although the ranking depends mildly on the observable, the three most important nuclear parameters are the vacuum value of the dilaton field $χ_0$ (which sets the overall scale of the scalar potential and trace-anomaly contribution), the scalar singlet strength $g_{1}^X$ (which controls the overall scalar attraction through the baryon effective masses), and the $k_0$ quadratic scalar term (which governs the curvature of the scalar potential). This framework provides a reproducible, data-driven approach to quantify parameter sensitivities in dense-matter models and to guide future Bayesian inference of nuclear information from multi-messenger astrophysical observations.
A minimal fractional deformation of Newtonian gravity
S. M. M. Rasouli
Published: 2026-03-16
Categories: gr-qc
We consider a minimal fractional deformation of Newtonian gravity characterized by a single parameter $α$. In the limit $α\to 1$, the theory reduces to standard Newtonian gravity. Previous works showed that the $Λ$CDM cosmology consistently emerges from this framework. Using a single potential, the model reproduces the full sequence of cosmic evolution (from a nonsingular pre--inflationary phase and a stable inflationary attractor to the radiation- and matter-dominated eras and the present accelerated expansion) and accounts for the growth of large-scale structure for $|α-1|\ll1$, in agreement with current observations. Here we show that the same fractional Newtonian model also describes key weak--field tests, including the perihelion precession of Mercury and the gravitational deflection of light, using a unified potential with the same constraint on $α$. These results suggest that the minimal fractional Newtonian framework may provide a unified phenomenological description of gravitational dynamics from Solar-System scales to cosmology. Finally, this fractional cosmological framework may offer new perspectives on problems such as the cosmological constant, the hierarchy of cosmological scales, and the Hubble tension.
Cosmological prospects for multiband detection of intermediate-mass binary black holes with Taiji and ground-based detectors
Yue-Yan Dong, Ji-Yu Song, Jing-Fei Zhang, Xin Zhang
Published: 2026-03-16
Categories: astro-ph.CO
Intermediate-mass black holes (IMBHs) bridge the gap between stellar-mass and supermassive black holes, but remain challenging to detect electromagnetically. Gravitational-wave observations provide a direct means of detecting IMBHs and their mergers. We simulate the gravitational-wave signals of IMBH binaries under different population models and assess their detectability with the space-based detector Taiji alone and in a multiband network combining Taiji with third-generation ground-based detectors. Taiji performs well in detecting high-mass IMBH binaries, while ground-based detectors compensate for its reduced sensitivity to lower-mass systems. Their combination expands the accessible parameter space and improves the constraints on cosmological parameters. In particular, multiband observations improve the constraint accuracy on $H_0$ by $36.5\%$ and $31.0\%$ compared with Taiji and ET2CE alone, respectively. We further examine the dependence of parameter accuracy on the number of simulated events, finding that improvements are most pronounced for small samples and gradually saturate as the number of events increases. We conclude that multiband observations enhance the detectability of IMBH binaries and reinforce their role as probes of precision cosmology.
Ringdown waves from hairy black holes
Ariadna Uxue Palomino Ylla, Kosuke Makino, Akane Tanaka, Akihiro Ishibashi, Chul-Moon Yoo
Published: 2026-03-16
Categories: gr-qc
We derive general formulas for quasi-normal mode (QNM) frequencies of hairy black holes by exploiting the QNM--geodesic correspondence. The black hole hair is treated as an anisotropic fluid perturbatively added to the vacuum black holes (Schwarzschild and Kerr black holes). Under this setting, independent of energy conditions, our formulas offer a systematic method to compute quasi-normal mode frequencies for a broad class of hairy black holes.
Non-metricity effects on electron scattering in bumblebee gravity
A. A. Araújo Filho
Published: 2026-03-16
Categories: gr-qc
We investigate non-metricity effects on electron scattering in metric-affine bumblebee gravity, where spontaneous Lorentz symmetry breaking is induced by a vector field acquiring a nonzero vacuum expectation value. Treating the affine connection as an independent variable and integrating it out leads to an effective description in which non-metricity modifies the dispersion relation of the bumblebee modes. From the full momentum-space propagator, we determine the pole structure that governs the interaction and construct the corresponding static Green function and interparticle potential. For a purely timelike background, the dispersion relation remains isotropic and produces a Coulomb potential with a uniformly rescaled effective coupling; consequently, the scattering amplitude preserves the Rutherford angular dependence, with the Lorentz-violating parameter entering only as an overall multiplicative factor. In contrast, a spacelike background induces anisotropy in the dispersion relation, leading to an orientation-dependent potential characterized by a quadrupolar modulation. This anisotropic structure propagates to the differential and integrated cross sections, introducing directional dependence while preserving the long-range character of the interaction. Finally, we consider phenomenological constraints from atomic physics. Hydrogen spectroscopy constrains the isotropic sector associated with the timelike configuration, whereas searches for anisotropies provide stronger limits on the quadrupolar contribution governed by $ξb^{2}$.
Reissner-Nordström Black Holes at second post-Minkowskian order from Scattering Amplitudes
Allan Alonzo-Artiles, Manfred Kraus
Published: 2026-03-16
Categories: hep-th
We employ one-loop scattering amplitudes in Einstein-Maxwell theory to compute the classical Hamiltonian of a binary system of two charged, non-spinning compact objects. The Hamiltonian is valid to all orders in velocity and up to second post-Minkowskian order (2PM), i.e. $\mathcal{O}(G^2)$. The classical interaction potential is extracted via matching to a non-relativistic classical effective field theory. We also provide the scattering angle at 2PM order. We perform several cross checks on our results and find full agreement with existing results in the literature. Finally, we also briefly discuss a comparison for the scattering angle, the binding energy and the periastron shift of a bound system up to the second post-Newtonian order.
Dark Energy with Constant Inertial Mass Density: Updated Constraints and Curvature-Induced Sign Transitions in $ρ_{\rm DE}$ and $ρ_{\rm DE}+p_{\rm DE}$
Luis A. Escamilla, Berat Karadavut, Nihan Katırcı
Published: 2026-03-16
Categories: astro-ph.CO
We present updated observational constraints on the simple-gDE model, characterized by a constant inertial mass density (IMD) $ρ_{\rm DE}+p_{\rm DE}$,which belongs to the broader graduated dark energy family, and compare its cosmological implications with those of the $w$CDM and the $Λ$CDM models. This parametrization provides a physically motivated, one-parameter extension of $Λ$CDM, perspective on DE dynamics beyond the usual equation-of-state approach. We use the newly released DESI DR2 BAO data in combination with either CMB measurements from Planck 2018 or late-time probes, CC and the Pantheon+ SNe Ia sample, considered both with and without SH0ES calibration in this analysis. The data favor a small positive IMD, and Bayesian evidence indicates that the models remain statistically indistinguishable within spatially flat scenarios. Consequently, none of these models exhibits a sign transition in the DE energy density, and no improvement in $H_0$ tension. Allowing spatial curvature qualitatively enlarges the phenomenology of the dark sector. In particular, the interplay between spatial curvature and a nonzero IMD permits sign transitions in both the effective dark-energy density and the IMD during cosmic evolution. For the BAO+CC+SN+SH0ES dataset, the $o$Simple-gDE model yields a transition redshift $z^\dagger = 1.51^{+0.68}_{-0.34}$, while the crossing of the Null Energy Condition boundary (NECB), defined by $ρ_{\rm DE}+p_{\rm DE}=0$, occurs at $z_{\rm NECB}=2.36^{+1.48}_{-1.48}$. The model is statistically favored over $oΛ$CDM and $ow$CDM. These results highlight the potential role of IMD as a fundamental parameter in DE phenomenology and demonstrate that geometric effects, such as spatial curvature, can reveal dynamical features of the dark sector that remain hidden within the spatially flat $Λ$CDM framework.
Gravitational-Wave Propagation Through the Axiverse
Leah Jenks, Marc Kamionkowski
Published: 2026-03-16
Categories: astro-ph.CO
We study the effects of oscillating, ultralight scalar and pseudoscalar fields on the propagation of gravitational waves (GWs). We consider two potential couplings of the (pseudo)scalars to gravity; a parity-even Gauss-Bonnet coupling, and parity-odd Chern-Simons coupling. We find several effects at both the population and individual GW event level, characterized by oscillatory features controlled by the (pseudo)scalar mass. In the parity-even case, this feature can be seen in the observed GW redshift and speed distributions, as well as in the dispersion relation and phase of individual events. We use the observation of the GW170817 multimessenger binary neutron star event to place constraints on the parity-even scalar-graviton coupling. In the parity-odd case, the effects are birefringent, but we find an overall washout of polarization at the population level. Oscillatory features can be seen in the observed GW amplitude and inclination distributions. Finally, we find that continuous, monochromatic GW sources are a promising target to observe these effects. The presence of a (pseudo)scalar field imprints a modulation of the GW waveform in the time domain, which can potentially be observed with space-based detectors such as LISA.
Quasi-pole quintessential inflation in metric-affine gravity
Konstantinos Dimopoulos, Christian Dioguardi, Ioannis D. Gialamas, Antonio Racioppi
Published: 2026-03-16
Categories: gr-qc
We study quintessential inflation in the framework of metric-affine gravity. It is well known that non-minimal couplings with the Holst invariant can generate a quasi-pole inflationary behaviour resulting in a Starobinsky-like phenomenology. The same quasi-pole behaviour can also be used in order to "flatten" the scalar potential in the Dark Energy era providing a successful framework for quintessential inflation. Agreement with all the observational constraints, reduces the predicted scalar spectral index to a narrow window: $0.966 \lesssim n_s \lesssim 0.967$, making the model highly testable and falsifiable.
Impact of numerical-relativity waveform calibration on parametrized post-Einsteinian tests
Simone Mezzasoma, Carl-Johan Haster, Nicolás Yunes
Published: 2026-03-16
Categories: gr-qc
Testing general relativity in the strong-field and highly dynamical regime is now possible through current gravitational-wave observations, where even a single high-quality detection can place competitive constraints on deviations from Einstein's theory. The parametrized post-Einsteinian framework provides a theory-agnostic approach to search for such deviations, but it typically assumes that systematic uncertainties in the base waveform model, particularly those arising from calibration to numerical relativity, are negligible. In this work, we investigate how calibration errors in the late-inspiral fitting coefficients of the IMRPhenomD waveform model can lead to spurious detections of departures from general relativity in parametrized tests. We use an uncertainty-aware version of IMRPhenomD, recalibrated to a set of numerical relativity surrogate waveforms and equipped with a probabilistic description of its fitting coefficients, to simulate general-relativity-consistent signals. We inject these signals into an O5 ground-based detector network and recover them with the original IMRPhenomD model augmented with a parametrized post-Einsteinian phase deformation. We find that false violations of general relativity using this model arise for network signal-to-noise ratios as low as 60. When the uncertainty-aware model is used instead, the inferred parametrized post-Einsteinian phase deformation remains consistent with zero even for signals with a signal-to-noise ratio up to 330. These results demonstrate the need to account for numerical relativity calibration uncertainty in order to perform reliable inspiral tests of general relativity. They also illustrate that explicitly incorporating numerical relativity calibration uncertainty into the waveform model preserves our ability to robustly test general relativity.
Observing Micro Black Hole Dark Matter
Manuel Ettengruber, Florian Kühnel
Published: 2026-03-16
Categories: hep-ph
Primordial micro black holes can constitute dark matter if short-distance gravity is modified by extra dimensions or a large number of species and if the memory-burden effect sufficiently suppresses Hawking evaporation. The resulting black holes in the transition regime differ from their four-dimensional Einsteinian counterparts through their mass--radius relation, temperature, entropy, and lifetime, which can render even very light objects cosmologically stable. The most promising observational consequences of such micro black holes dark matter are analysed. Neutron star survival yields the most robust constraints, while a narrow region of parameter space can simultaneously remain viable and address the missing-pulsar problem in the Galactic center. Diffuse evaporation signals in neutrino telescopes are found to be relevant mainly in extra-dimensional scenarios, whereas in generic species models, visible emission is strongly suppressed by evaporation into dark sectors. Merger-induced evaporation bursts can provide an additional probe in extra-dimensional realisations if the post-merger remnant briefly returns to the semiclassical phase. Overall, micro black holes dark matter remains phenomenologically viable in constrained regions, with neutron stars, neutrino telescopes, and merger signatures providing complementary tests.
Hankel low-rank matrix approximation for gravitational-wave data analysis
Nicholas Geissler, Vladimir Strokov, Christian Kümmerle, Sergey Kushnarev, Emanuele Berti
Published: 2026-03-16
Categories: astro-ph.HE
Next-generation gravitational-wave (GW) detectors, such as the Laser Interferometer Space Antenna (LISA), will observe vast numbers of overlapping signals. Disentangling these signals from instrumental noise and from one another constitutes a significant data analysis challenge. We explore a denoising technique based on embedding time series into Hankel matrices: a superposition of $n$ (damped) sinusoids corresponds to a matrix of rank $2n$. Thus, the problem of signal extraction is reduced to a structured low-rank approximation problem. Using synthetic data tailored to GW applications, we benchmark three Hankel-based algorithms: ESPRIT, Cadzow iterations, and iteratively reweighted least squares (IRLS). Our test scenarios include isolated and multi-component monochromatic signals, the resolution of sources with closely spaced frequencies, and the recovery of black hole quasinormal modes (QNM). All three algorithms achieve near-optimal performance consistent with Fisher matrix bounds, evidenced by an inverse-square scaling of the mismatch with the signal-to-noise ratio. Furthermore, a proof-of-concept application to numerical relativity waveforms validates the ability of these algorithms to extract QNM frequencies from ringdown signals. Hankel low-rank approximation therefore offers a transparent, computationally efficient avenue for preprocessing GW time series.
Crowdsourcing Gravitational Waves from Superradiant Axions
Sebastian A. R. Ellis, Orion Ning, Nicholas L. Rodd, Jan Schütte-Engel
Published: 2026-03-16
Categories: hep-ph
Black hole superradiance is a powerful probe of ultralight axions. If nature contains a boson with a mass of order $10^{-12}\,$eV, $\textit{mere vacuum fluctuations}$ will lead to its efficient production around spinning stellar mass black holes, forming a gravitational atom that both drains the black hole spin and decays to produce near-monochromatic gravitational waves. Existing superradiance constraints derive primarily from spin measurements of a handful of identified black holes. Here we instead present a detailed study of the population level effect: gravitational waves arising from both the 100 million black holes in the Milky Way and the stochastic signal from axion clouds throughout the universe. We study the impact of a broad range of systematic uncertainties on the black hole properties and compute the projected axion sensitivity for LIGO, as well as the future instruments Einstein Telescope, Cosmic Explorer, and a high-frequency Magnetic Weber Bar. We demonstrate that LIGO can robustly probe axion masses from roughly $10^{-13}\,$eV to $4 \times 10^{-12}\,$eV. If the black hole population extends to masses slightly below $5\,M_{\odot}$ - as hinted for by LIGO inspiral observations - LIGO would approach $10^{-11}\,$eV. Under that same assumption we show that a future high-frequency detector could push considerably higher, potentially beyond $10^{-10}\,$eV in the most optimistic scenarios, reaching towards the lowest masses within the projected sensitivity of axion dark matter searches.
Exact Path Integral Methods in Supersymmetric $\text{AdS}_2\times \mathbf{S}^2$ Backgrounds
Alberto Castellano, Carmine Montella, Matteo Zatti
Published: 2026-03-16
Categories: hep-th
We determine the exact functional determinants of charged, massive spin-0 and spin-$\frac12$ particles in $\text{AdS}_2\times \mathbf{S}^2$ backgrounds threaded by constant electric and magnetic fields. This is achieved using Schwinger proper-time formalism, which allows us to derive the full non-perturbative effective action in the 1-loop and constant background field approximations. We then specialize the computation to supersymmetric settings and we obtain the effective action for a 4d $\mathcal{N}=2$ BPS massive hypermultiplet in a supersymmetric $\text{AdS}_2\times \mathbf{S}^2$ spacetime. This setup can be seen to be equivalent to the near-horizon geometry of a BPS black hole which solves the attractor equations of 4d $\mathcal{N}=2$ supergravity. Our results provide a necessary intermediate step for the evaluation of the quantum-corrected black hole partition function. We also comment on the relation with the celebrated Gopakumar-Vafa integral representation.
Bouncing geodesics, black hole singularities, and singularities of thermal correlators
Sašo Grozdanov, Samuel Valach, Mile Vrbica
Published: 2026-03-16
Categories: hep-th
Bouncing geodesics have been used as valuable probes of black hole singularities. In the dual boundary theory, the presence of bouncing geodesics is encoded in the analytic structure of correlation functions. Thus, when their existence is related to the presence of a black hole singularity, this presents a practical holographic framework to analyse, diagnose, and classify spacetimes with curvature singularities. To make this intuition precise, we use the Hadamard theory of hyperbolic differential equations to prove that both bulk and boundary retarded propagators diverge whenever two points can be connected by a null geodesic. We clarify why this statement remains valid beyond the geodesic regime (for operators of any dimension) and examine how holographic renormalisation modifies the structure of the dual propagator. We also present a general characterisation of bouncing geodesics and the associated singularities in correlation functions for arbitrary spacetimes. Furthermore, we compare the analytic structure of the correlators in position and momentum space and discuss explicit examples. Finally, we demonstrate the validity and concrete limitations of the bouncing geodesic approach to the study of black hole singularities. In particular, we show an explicit example of a black hole in the self-dual linear axion model, which has a curvature singularity despite the absence of bouncing geodesics.
Probing Gravitational-Wave Four-Point Correlators
Martina Ciprini, Maria Lucia Marcelli, Gianmassimo Tasinato
Published: 2026-03-16
Categories: astro-ph.CO
Stochastic gravitational-wave backgrounds (SGWBs) of primordial origin offer a powerful probe of early-Universe physics and possible dark-sector dynamics. While most searches focus on the GW power spectrum, additional information is encoded in higher-order correlators that characterize the statistical properties of the signal. In this work we study non-Gaussian features of a cosmological SGWB generated at second order by vector fluctuations, a class of sources well motivated in early-Universe scenarios. Within this framework we develop tools to characterize higher-order GW correlators and compute representative four-point functions that generate a connected contribution to the GW trispectrum. We show that the trispectrum amplitude scales as the square of the GW power spectrum and peaks in characteristic folded momentum configurations, reflecting the structure of the nonlinear source. We then explore the observational implications. First, we demonstrate that the connected trispectrum contributes to the variance of two-point overlap reduction functions, including the Hellings-Downs curve relevant for pulsar timing arrays. We then construct the optimal estimator to measure the connected trispectrum with ground-based interferometers. Our results highlight how non-Gaussian SGWB statistics provide a complementary observable to probe the origin of GW backgrounds and to distinguish cosmological from astrophysical sources.
Direct Waves in Black-Hole Binary Mergers: Insights from the Backwards One Body Model
Anuj Kankani, Sean T. McWilliams
Published: 2026-03-16
Categories: gr-qc
The merger-ringdown radiation from a black hole binary merger is accurately modeled by a sum of linear quasinormal modes (QNMs). Recently, a non-QNM ``direct wave" component of the radiation, associated with prompt emission from a plunging perturber, has been identified. Motivated by the behavior of null geodesics perturbed from the remnant light ring, the Backwards One Body (BOB) approach has been shown to model the full merger-ringdown radiation to high accuracy, while using only a minimal number of parameters. In this work, using the Pöschl--Teller potential, we first show how the BOB amplitude evolution can be recovered from the QNM pole contributions. We then apply rational filters to isolate the non-QNM content in BOB and numerical relativity waveforms. We show that BOB naturally captures the direct wave component of the merger radiation, explaining its accuracy near the waveform peak. Finally, we use BOB to show that the direct wave frequency is largely uncorrelated with the horizon frequency, even for high spin remnants, and instead tracks the News frequency at the time of the peak News amplitude.
Approximate Models for Gravitational Memory
Q-L Zhao, P. -M. Zhang, M. Elbistan, P. A. Horvathy
Published: 2026-03-16
Categories: gr-qc
The large-distance development of a sandwich gravitational wave, consistent with Carroll symmetry, provides us with a surprisingly good analytic approximation of the motion of particles in a wave with Pöschl-Teller profile. The role of the 2nd solution of the Stern-Liouville equation is highlighted. Similar results hold for Gaussian profiles.
A numerical framework for Newtonian-noise estimation at the Einstein Telescope: 2-D simulations beyond the plane-wave approximation
Patrick Schillings, Shi Yao, Johannes Erdmann, Andreas Rietbrock
Published: 2026-03-16
Categories: astro-ph.IM
The Einstein Telescope (ET) is a third-generation underground gravitational-wave observatory designed to extend the detection sensitivity down to a few Hertz. Newtonian noise is expected to limit the low-frequency sensitivity of ET, particularly in the 1.7-6 Hz band. Most existing estimates rely on analytical or semi-analytical models assuming homogeneous or layered media, neglecting geological heterogeneity and complex wave interactions. In this work, we present a numerical framework for Newtonian-noise estimation based on spectral-element simulations of a seismic wave field. As a proof of concept, we first benchmark the numerical results against analytical plane-wave predictions in a two-dimensional homogeneous medium with a single surface source, demonstrating excellent agreement for both bulk and cavern contributions. We then extend the model to an array of 30 stochastic surface sources to approximate stationary ambient seismic excitation. The P-wave fraction inferred from the simulated wave field is, in this simple homogeneous case, significantly lower than commonly assumed, indicating enhanced prospects for Newtonian-noise mitigation. The framework is readily applicable to three-dimensional simulations and to integration of detailed local seismic models and topography, offering strong potential for site-specific Newtonian-noise estimation.
When One-Parameter Dark Energy Makes Neutrinos Physical Again
Weiqiang Yang, Eleonora Di Valentino, Eric V. Linder, Sibo Zhang, Supriya Pan
Published: 2026-03-16
Categories: astro-ph.CO
A puzzling implication of current data interpreted in the $Λ$CDM cosmology is the preference for a negative sum of neutrino masses. Moving to $w_0w_a$CDM brings an appreciable fraction of the neutrino mass posterior back to positive values, while the constant equation-of-state dark energy case $w$CDM does not. We investigate a variety of one-parameter dark energy equations of state (DE EoS), each variation with particular physical properties, to understand whether a two-parameter DE EoS is required to bring the neutrino mass positive. The conclusion is that certain one-parameter DE EoS can suffice, implying that the data are pointing toward physical characteristics rather than a broad degeneracy. The required characteristics are identified as phantom dark energy at high redshift, crossing $w=-1$ at lower redshift.
Classical Gravitational Scattering from the Ultraviolet and the Absence of Calabi-Yau Integrals in the Conservative Sector at $O(G^5)$
Zvi Bern, Avery Jackman, Gareth Mansfield, Michael S. Ruf
Published: 2026-03-16
Categories: hep-th
We explain why Calabi-Yau and complete elliptic integrals do not contribute to conservative observables at fifth post-Minkowskian order, despite appearing in intermediate steps. At even loop orders, conservative contributions are tied to terms proportional to the logarithm of the momentum transfer, which in dimensional regularization arise from singular regions. We show that in the classical limit, the integral classes responsible for Calabi-Yau and complete elliptic behavior are absent from the ultraviolet singular structures that generate the required logarithm. This perspective also suggests alternative strategies for analyzing the classical limit of multiloop integrals in the conservative sector at even loop orders.
Plasma impact on black hole shadow and gravitational weak lensing for Schwarzschild-like black hole
Weiqiang Yang, Mirzabek Alloqulov, Ahmadjon Abdujabbarov, Bobomurat Ahmedov, Chengxun Yuan, Chen Zhou
Published: 2026-03-16
Categories: gr-qc
This article delves into the observational properties of a Schwarzschild-like black hole (BH). Initially, the research provides a succinct examination of the spacetime geometry and the configuration of its horizon. Furthermore, we study the photon dynamics around the Schwarzschild-like BH in the presence of the plasma using the Hamiltonian formalism. It was found that the photon sphere radii increase under the influence of the plasma frequency and vice versa for the spacetime parameters. Further exploration is dedicated to understanding how the plasma affects the shadow of the BH, and we find that the radius of the BH shadow shrinks with the rise of the $ξ$ parameter and plasma frequency. We then turn to the getting constraint of the spacetime parameters and the plasma frequency by using the observational data released by the Event Horizon Telescope (EHT) collaboration for the M87* and Sgr A*. Additionally, the research scrutinises the phenomenon of gravitational weak lensing in the vicinity of a Schwarzschild-like BH, considering both uniform and non-uniform plasma scenarios. The outcomes demonstrate that the angle of deflection increases under the influence of a uniform plasma frequency, whereas the opposite is true for non-uniform plasma. In both scenarios, a rise in the spacetime parameters results in a decrease in the deflection angle. Finally, we investigate the magnification of the gravitationally lensed image. The effect of the spacetime parameters and plasma frequencies on the total magnification are same as in the deflection angles.
Informational corrections to the early-Universe radiation sector: CET Omega, WIMP freeze-out, and implications for a possible 20 GeV gamma-ray excess
Christian Balfagon
Published: 2026-03-16
Categories: astro-ph.HE
Recent analyses of Fermi-LAT data have identified a nearly spherical, halo-like excess of gamma rays peaking at E_gamma ~ 20 GeV. If interpreted as dark matter annihilation, the excess directly probes the thermal freeze-out epoch and therefore any non-standard corrections to the early-Universe expansion rate. In this work we examine the implications of this tentative signal for CET Omega, an informational and modular extension of relativistic quantum field theory and cosmology. CET Omega predicts a universal state-dependent modification to the radiation energy density of the early Universe, characterized by a doubly logarithmic correction originating from renormalized modular fluctuations in the spectral triple of the theory. The correction is negligible during Big Bang nucleosynthesis and recombination but becomes relevant during thermal WIMP freeze-out. We derive the correction from the modular two-point function, justify the onset scale associated with the informational sector, and compute its quantitative impact on freeze-out through numerical solutions. We also analyze the evolution of the informational field Phi_Omega(x) and show that it freezes in before the freeze-out epoch and survives to the present time under gravitational advection. The resulting modification induces percent-level shifts in the relic abundance and sub-percent morphological corrections to the annihilation gamma-ray flux. We compare the scenario with Early Dark Energy, kination, and varying N_eff models, and show that the parameter range 10^{-4} < alpha_log < 10^{-2} remains consistent with Planck, BBN, and BAO constraints while predicting potentially observable deviations in the gamma-ray morphology accessible to next-generation MeV-GeV missions.
Viaggiu holographic dark energy in light of DESI DR2
Amlan K. Halder, Andronikos Paliathanasis, Stefano Viaggiu, Abdulla Al Mamon, Subhajit Saha
Published: 2026-03-16
Categories: gr-qc
We test the cosmological viability of the Viaggiu holographic dark energy (VHDE) model by using late-time observational data. In particular, we place constraints on the free parameters of the model using Type Ia supernovae from the PantheonPlus, Union3.0, and DES-Dovekie catalogues, the Cosmic Chronometers, and the Baryon Acoustic Oscillations from the DESI DR2. Our analysis suggests that the VHDE model fits the observational data better or similar to the $Λ$CDM for all dataset combinations considered. The value obtained for $H_0$ is similar to the $Λ$CDM, while the current matter density parameter is constrained around $Ω_{m0}\simeq 0.24$, smaller to that obtained by the $Λ$CDM. Moreover, the parameter introduced by the VHDE is found to have a mean value within the range $\fracπ{3} δ^2 \sim 0.27-0.33$. Finally, we used Akaike's Information Criterion (AIC) and Bayesian evidence to test the VHDE model against the $Λ$CDM scenario. The AIC demonstrates that the two models are statistically indistinguishable, while Bayesian evidence reveals that the data have a mild preference for the $Λ$CDM model for most of the dataset combinations considered. Nevertheless, the VHDE model remains consistent with current late-time cosmological observations and offers a feasible mechanism for describing the late-time accelerating scenario.
py5vec: a modular Python package for the 5-vector method to search for continuous gravitational waves
Luca D'Onofrio, Federico Muciaccia, Lorenzo Mirasola, Matthew Pitkin, Cristiano Palomba, Paola Leaci, Francesco Safai Tehrani, Francesco Amicucci, Lorenzo Silvestri, Lorenzo Pierini
Published: 2026-03-16
Categories: astro-ph.IM
We present \texttt{py5vec}, a Python package for implementing and extending the 5-vector method, used to search for continuous gravitational wave (CW) signals. We also provide a comprehensive theoretical review of the 5-vector method and extend the relative likelihood formalism by marginalizing over the noise variance, resulting in a more robust Student's t-likelihood, and over the initial phase to account for pulsar glitches. \texttt{py5vec} provides a modular architecture that separates data representation, signal demodulation, and statistical inference into independent abstract stages. It supports multiple input data formats and interoperates with existing Python software, providing a bridge between different approaches. For example, using a \texttt{bilby}-based interface, \texttt{py5vec} implements Bayesian parameter estimation within the 5-vector formalism for the first time. The modular design also allows for making exact multi-level and direct comparisons between other software, such as \texttt{cwinpy} and \texttt{SNAG} in MATLAB. In \texttt{py5vec}, we implement a multidetector targeted search for known pulsars, validated using LIGO data from the O4a run and hardware injections, demonstrating consistent reconstruction of signal parameters. This package therefore provides a flexible platform for current targeted searches and for future extensions to other CW search strategies.
Luminosity-Temperature Relation as a Probe for Modified Gravity
Antonino Del Popolo, Saeed Fakhry, David F. Mota
Published: 2026-03-16
Categories: astro-ph.CO
We investigate the luminosity-temperature ($L$-$T$) relation of galaxy clusters as a probe for testing modified gravity (MG) theories, focusing on $f(R)$ gravity and symmetron models. Using an improved semi-analytic framework that incorporates angular momentum acquisition, dynamical friction, and shock heating within the modified punctuated equilibrium model, we compare predictions against hydrodynamical simulations and observational data. While massive clusters remain largely screened and follow standard $Λ$CDM predictions, low-mass systems ($kT \lesssim 1-2$ keV) exhibit systematic deviations characterized by steeper $L$-$T$ slopes in MG scenarios. Crucially, we demonstrate that these signatures cannot be mimicked by conventional astrophysical processes such as feedback or angular momentum effects, which primarily affect normalization rather than curvature. Our results establish the $L$-$T$ relation as a robust diagnostic tool for distinguishing general relativity from screened MG theories, with the strongest discriminatory power emerging at group scales accessible to current and future X-ray surveys. Moreover, a normalized reduced $χ^2$ analysis of the $L$-$T$ relation shows that MG models provide significantly better agreement with observational data than $Λ$CDM, with several realizations achieving excellent fits while the $Λ$CDM model consistently performs worst.
The peculiar case of the Viaggiu holographic dark energy
Somnath Saha, Subhajit Saha, Nilanjana Mahata
Published: 2026-03-16
Categories: gr-qc
We study the plausibility of a holographic dark energy (HDE) model using the form of horizon entropy proposed by Viaggiu in 2014. This form of entropy is a generalization of the usual Bekenstein-Hawking entropy, having an extra term arising due to the dynamical nature of horizons in an expanding universe. We examine this new HDE model in the context of a flat Friedmann-Lemaître-Robertson-Walker universe filled with two cosmic fluids -- dark matter in the form of dust and holographic dark energy generated by Viaggiu entropy. We consider the Hubble horizon and the future event horizon as characteristic length scales and study the evolution of the Universe within these frameworks. Our analysis reveals some intriguing findings that include a possible cosmic doomsday scenario in the future, and certain observations are in striking contrast to other HDE models studied in the literature.
Parametrizing superfluid dark matter with rational approximations
Francesco Lottatori
Published: 2026-03-16
Categories: gr-qc
We investigate how a spatially modulated real scalar background $φ(\vec{x})$ can modify phonon propagation in the context of Superfluid dark matter (SFDM). Using a simple toy model with quartic condensate and coupling $-gφ^2|Ψ|^2$, we derive the local equation of state and the effective sound velocity $c_s(\vec{x})$. For $g>0$, modulation tends to increase the effective mass of the condensate and make the medium less rigid, suppressing $c_s^2\propto m_{Ψ,\mathrm{eff}}^{-4}$ up to a ``dust-like'' regime, $c_s^2\to 0$. We implement this modulation for the background scalar field by imposing rational profiles, through Padé radial profiles, and show the corresponding variation of $c_s^2(r)$ for different $g$, discussing implications for the structure of SFDM cores and the possible formation of inhomogeneous regions of dark matter.
Inflation without an Inflaton III: non-Gaussian signatures
Mariam Abdelaziz, Marisol Traforetti, Daniele Bertacca, Raul Jimenez, Sabino Matarrese, Angelo Ricciardone
Published: 2026-03-16
Categories: astro-ph.CO
We investigate primordial non-Gaussianity in the Inflation without an Inflaton (IWI) framework, where scalar perturbations are generated at second order by primordial gravitational waves in Einstein gravity on an exact de Sitter (dS) background. Since scalar modes are produced nonlinearly from tensor modes, non-Gaussianity is an intrinsic prediction of the mechanism. We compute the corresponding scalar bispectrum, derive the relevant contribution to the three-point function of the scalar potential, and evaluate its shape numerically. We find that, unlike the scalar power spectrum, the bispectrum depends logarithmically on the ultraviolet cutoff set by the end of inflation, indicating a structural difference between the two- and three-point statistics in this scenario. Its shape is enhanced toward squeezed configurations, but its amplitude becomes strongly suppressed once the scalar power spectrum is normalized to the observed value. The resulting non-Gaussianity at CMB scales is therefore negligibly small, well below present observational sensitivity.
Optical Magnus effect on gravitational lensing
Yusuke Nishida
Published: 2026-03-16
Categories: gr-qc
The optical Magnus effect refers to transverse shift of a trajectory of light caused by its polarization and appears as a correction to geometrical optics at the linear order in wavelength. Here, we start from Maxwell's equations in a curved spacetime to derive the equation of motion for a wave packet of circularly polarized light, which confirms the known result involving the helicity-dependent anomalous velocity with some generalization and clarification. We then study possible consequences of the optical Magnus effect on gravitational lensing in the Schwarzschild spacetime as well as under a weak gravitational potential in an expanding spacetime. Among others, by formulating the lens equation modified to incorporate the optical Magnus effect, the Einstein ring is found impossible to emerge from a point source for any axially symmetric thin lens. Analytic solutions to the modified lens equation are also obtained for simple lens models, illuminating how image formation is affected by the optical Magnus effect.
Spectral Bifurcations in Quasinormal Modes of Regular BTZ Black Holes
Kartheek Hegde, Tajron Jurić, A. Naveena Kumara
Published: 2026-03-16
Categories: gr-qc
We study the quasinormal spectrum of massless scalar fields propagating on a family of regular BTZ black holes arising from an infinite tower of dimensionally regularized Lovelock corrections. These geometries are asymptotically AdS, reduce to the standard BTZ solution in the limit $\ell \to 0$, and resolve the central singularity by introducing a smooth core controlled by the new length scale $\ell$. The scalar quasinormal modes are computed using both Leaver's continued-fraction method and the Horowitz-Hubeny power-series method; the two approaches agree to high accuracy across the parameter space. We find that the regularization preserves linear stability ($ω_I < 0$) while qualitatively reshaping the spectrum: as $\ell$ increases, BTZ-like complex branches collide with the imaginary axis and undergo a hierarchy of bifurcations into multiple purely imaginary branches, leading to mode switching and a nontrivial reordering of overtones as functions of $\ell$ and the harmonic index $m$. Our results place regular BTZ black holes within the emerging family of bifurcating quasinormal spectra known from nearly extremal and asymptotically AdS black holes, and highlight these $(2+1)$-dimensional geometries as a controlled arena for exploring geometric mechanisms behind spectral branching and late-time ringdown in regular black hole spacetimes.
Cosmological angular momentum from quantum rotation
Bo-Qiang Lu
Published: 2026-03-16
Categories: gr-qc
The origin of cosmic angular momentum is a fundamental question in structure formation. We propose a novel mechanism that generates spatial angular momentum directly from quantum fluctuations during inflation. A spectator complex scalar field with global U(1) symmetry stores internal angular momentum via field-space rotation. Inflationary perturbations create spatial gradients that, upon horizon re-entry, couple to the background charge density and source a bulk momentum flow. During nonspherical gravitational collapse, this flow converts into net angular momentum. For primordial black holes forming from such collapse, the dimensionless spin can reach \(χ\sim 0.1-1\) when the small-scale power spectrum is enhanced to produce detectable abundances-far exceeding tidal torque theory predictions. This establishes a testable link between inflation, primordial perturbations, and black hole spin distributions accessible to gravitational-wave observations.