Preprints in GR/QC

Christopher Gerlach, Yann Gouttenoire, Antonio J. Iovino, Nicholas Leister

Published: 2025-08-11

Categories: astro-ph.CO

We show that primordial black holes (PBHs) in the $\textit{Stupendously Large Black Hole}$ mass range ($M \gtrsim 10^{11}\,M_\odot$) produce isocurvature perturbations exceeding current $\textit{Planck}$ Cosmic Microwave Background limits, thereby excluding them as a significant dark matter component.

R. Prasad, Anushka Doke, Prayush Kumar

Published: 2025-08-11

Categories: astro-ph.HE

We study the imprint of magnetic fields on gravitational waves emitted during the inspiral phase of eccentric binary neutron star systems. While observations indicate that neutron stars typically exhibit strong magnetic fields in the range of $10^{14}$-$10^{15}\,\mathrm{G}$, theoretical models allow for fields as high as $ \sim 10^{17-18}\,\mathrm{G}$. In binaries, the fate of these fields depends on the formation pathway: in systems formed through isolated evolution, magnetic fields may decay over long inspiral timescales. In contrast, binaries formed via dynamical capture can retain substantial eccentricity and strong fields until merger, potentially altering the gravitational waveform. We consider two magnetic effects: magnetic interaction between the neutron stars and electromagnetic radiation from the system's effective dipole, and identify regimes where each dominates. Using a perturbative framework, we compute the associated energy loss and gravitational wave phase evolution. We find that for binaries with strong and comparable magnetic fields, $10^{14}\,\mathrm{G}$ fields may be detectable up to $\sim 10 \, \mathrm{Mpc}$ with DECIGO and the Einstein Telescope, while $10^{15}\,\mathrm{G}$ fields extend the reach to several hundred Mpc. For extreme fields of $10^{16}\,\mathrm{G}$, third-generation detectors could be sensitive out to Gpc scales. In contrast, LIGO is limited to galactic distances: $10^{15}\,\mathrm{G}$ fields are detectable only within $\sim 100\,\mathrm{kpc}$, and only ultrastrong fields ($\sim 10^{16}$-$10^{17}\,\mathrm{G}$) are potentially observable at Gpc distances. In highly asymmetric systems, where dipole radiation dominates, the gravitational wave dephasing is significantly suppressed, reducing the detection horizon. These findings suggest that current and future gravitational wave observatories may be capable of identifying magnetized binary systems.

Sivasish Paul, Raj Kumar Das, Supriya Pan

Published: 2025-08-11

Categories: astro-ph.CO

In the present article, we propose a very simple parametrization of the Hubble function without parametrizing the dark components of the Universe. One of the novelties of the parametrization is that it may include a wide variety of the cosmological models, such as dark energy (both noninteracting and interacting fluids), modified gravity, cosmological matter creation and other known scenarios. The model is constrained with the latest astronomical probes from Hubble parameter measurements, three distinct versions of Type Ia Supernovae (Pantheon+, DESY5, Union3) and baryon acoustic oscillations from Sloan Digital Sky Survey and Dark Energy Spectroscopic Instrument data releases 1 and 2. Our results suggest a mild deviation from the standard $\Lambda$CDM cosmological model for most of the combined datasets. We also find that our model is thermodynamically consistent and performs well in the model comparison tests.

G. E. Volovik

Published: 2025-08-11

Categories: gr-qc

The event horizon is a source of irreversibility, analogous to statistical irreversibility. This is why for systems with an event horizon there is no difference between quantum and thermal fluctuations. Quantum processes of quantum tunneling determine the thermodynamics of these systems, their temperatures, entropies and fluctuations. We considered three examples of entropy variance that support this point of view: (i) the variance of the area of the black hole horizon, obtained by consideration of quantum fluctuations; (ii) the variance of the entropy of the Hubble volume in the de Sitter state, obtained by consideration of thermal fluctuations; and (iii) the variance of entropy in integers in the Planckon model, determined by the Poisson distribution.

Sukhdeep Singh Gill

Published: 2025-08-11

Categories: astro-ph.CO

The bispectrum, being sensitive to non-Gaussianity and mode coupling of cosmological fields induced by non-linear gravitational evolution, serves as a powerful probe for detecting deviations from General Relativity (GR). The signatures of modified gravity in the bispectrum are even more pronounced in redshift space, where anisotropies from peculiar velocities provide unbiased information on higher-order properties of gravity. We investigate the potential of all non-zero angular multipoles $B_l^m$ of redshift space bispectrum across all possible triangle configurations to probe degenerate higher-order scalar tensor (DHOST) theory. We show that the higher-order multipoles of the bispectrum with $l=2,4,6$ are more sensitive to the modifications in gravity than the spherically averaged monopole moment $l=0$. These multipoles demonstrate remarkable sensitivity to the higher-order growth history, which varies across triangle configurations, with acute triangles generally being the most sensitive to modification in GR. The values of various multipoles exhibit opposite signs in modified gravity compared to those predicted in GR, which serves as a robust indicator of the deviation from GR. We demonstrate that, unlike $l=2$ and $4$ multipoles, the $l=6$ multipoles with $m\leq 4$ are not affected by the quadratic bias and second-order tidal bias parameters, emphasising the need to leverage their capabilities in analyses. The $(l=6, m > 4)$ multipoles fail to capture the second-order growth, while all $l=8$ multipoles lack any independent information regarding modified gravity in both linear and nonlinear regimes.

Shengzhi Li, Yongge Ma, Faqiang Yuan, Xiangdong Zhang

Published: 2025-08-11

Categories: gr-qc

The five-dimensional loop quantum Kaluza-Klein cosmology is constructed based on the symmetric reduction of the connection formulation of the full theory. Through semiclassical analysis, the effective scalar constraint for the cosmological model coupled with a dust field is derived, incorporating the quantum fluctuations of geometry as a subleading order correction. It demonstrates that the quantum model has the correct classical limit. The explicit solutions to the equations of motion show that the classical big bang and past big rip singularities in the classical model are avoided by a quantum bounce and a quantum collapse respectively in the effective model. In a particular scenario, the dynamical compactification of the extra dimension is realized, while the observable four-dimensional universe transitions through three distinct epochs: (i) a super-inflationary phase generating 55 e-folds with particular choices of the initial value, (ii) a decelerated expansion era, and (iii) a late-time accelerated expansion phase driven by quantum fluctuations. These results suggest that both cosmic inflation and dark energy may originate from the interplay between the compactified extra dimension and quantum geometric effects.

Leif Lui, Alejandro Torres-Orjuela, Rudrani Kar Chowdhury, Lixin Dai

Published: 2025-08-11

Categories: astro-ph.HE

One prominent model for quasi-periodic eruptions (QPEs) is that they originate from extreme mass-ratio inspirals (EMRIs) involving stellar-mass objects orbiting around massive black holes and colliding with their accretion disks. We compute the gravitational wave signals from such a model, demonstrating that orbiter-disk interactions result in small frequency shifts and high-frequency tails due to the excitation of non-discrete modes. Interestingly, we show that QPE RX J1301.9+2747 could be detectable by future space-based gravitational wave detectors, provided a moderate eccentricity around $0.25$ and a mass exceeding $35\,M_\odot$ for the orbiter. Moreover, based on this QPE model, we show that the signal-to-noise ratio of the gravitational wave signals from QPEs, if detectable, will be sufficiently high to distinguish such systems from vacuum EMRIs and shed light on the origin of QPEs and environments around massive black holes.

Julian Rapp, Radhika H. Joshi, Alwin van Steensel, Yuli V. Nazarov, Mohammad H. Ansari

Published: 2025-08-11

Categories: quant-ph

Many important quantities in quantum information science, such as entropy and entanglement, are non-linear functions of the density matrix and cannot be expressed as operator observables. Standard open-system approaches evolve only a single copy of the density matrix, making it impossible to track the dynamics of such quantities. A formalism proposed by some of the present authors addressed this challenge by evolving multiple virtual replicas, but was limited to the weak-coupling regime. Here, we extend this approach to strong coupling between a quantum system and classical environments. The resulting multi-replica master equation enables direct evaluation of entropy flow and related metrics in strongly hybridized quantum-classical systems. Our results show that quantum coherence and hybridization jointly suppress net entropy transfer, creating a thermodynamic bottleneck. This framework provides a general tool for studying entropy dynamics and guiding the design of more robust, resource-efficient quantum hardware.

Gorima Bezboruah, Mozib Bin Awal, Prabwal Phukon

Published: 2025-08-11

Categories: gr-qc

We study the thermodynamic phase transition of ModMax anti-de Sitter (AdS) black holes using Lyapunov exponents of massless and massive particles in unstable circular orbits. Our results demonstrate that the thermal profile of the Lyapunov exponent serves as an efficient probe of the black hole's phase structure. We calculate the discontinuity in the Lyapunov exponent across the transition and show that it acts as an order parameter, exhibiting a critical exponent $\delta=1/2$ in the vicinity of the critical point. Furthermore, we explore the violation of the chaos bound, finding that the bound is violated when the horizon radius falls below a threshold value. We also examine how the ModMax parameter and the particle's angular momentum modify this threshold, revealing their role in controlling the onset of chaos bound violation.

Nitesh K. Dubey, Sanved Kolekar

Published: 2025-08-11

Categories: gr-qc

We construct a smooth trajectory in Minkowski spacetime that is inertial in the asymptotic past and future but undergoes approximately uniform acceleration for a finite duration. In a suitable limit, this trajectory reduces to the standard Rindler trajectory, reproducing the expected Bogoliubov transformations and results consistent with the thermal time hypothesis. We analyze the behavior of an Unruh-DeWitt (UDW) detector following such a trajectory and explore the dependence of complete positivity (CP) divisibility on the detector's frequency, acceleration, and the duration of acceleration. Notably, we find that the detector exhibits a memory effect due to the finite duration of acceleration, which is also quantified by the Fisher information. We further examine two UDW detectors along various trajectory combinations and show that, unlike the transition rate, both the total correlation and the entanglement harvested return smoothly to their initial values after the acceleration/deceleration phase. These correlation measures behave similarly in both accelerating and decelerating segments. Interestingly, negativity and mutual information remain unaffected by the memory effect. We also discuss the physical significance of the sign of the flux of acceleration-induced radiation.

Yu. V. Shtanov, T. -H. O. Pokalchuk, S. G. Sharapov

Published: 2025-08-11

Categories: cond-mat.mes-hall

We investigate the Sagnac and Mashhoon effects in graphene, taking into account both the pseudospin and intrinsic spin of electrons, within a simplified model of a rotating nanotube or infinitesimally narrow ring. Based on considerations of the relativistic phase of the wave function and employing the effective Larmor theorem, we demonstrate that the Sagnac fringe shift retains a form analogous to that for free electrons, governed by the electron's vacuum mass. In the case of a narrow ring, an additional $\pi$-phase shift arises due to the Berry phase associated with the honeycomb graphene lattice. The Mashhoon fringe shift, which characterizes the dynamics of intrinsic spin, retains its conventional form in graphene, with its dependence on the Fermi velocity. Our analysis highlights both the similarities and differences between spin and pseudospin degrees of freedom in graphene.

Junbin Li

Published: 2025-08-11

Categories: gr-qc

We show that the $k$-self-similar naked singularity solutions of the spherically symmetric Einstein--Scalar field system are unstable to black hole formation under perturbations that are totally supported in the interior region, in all regularities strictly below the threshold. The instability below the threshold is also established for exterior perturbations. We also show that general naked singularity solutions are unstable under interior BV perturbations, which provides a new insight into understanding the weak cosmic censorship conjecture for this model. In contrast to all previous results on the exterior instability of naked singularities (and even trapped surface formation), where only a single incoming null cone is considered, the novel approach to proving the interior instability is analyzing a family of incoming null cones becoming more and more singular.

Takanori Anegawa, Kotaro Tamaoka

Published: 2025-08-11

Categories: hep-th

We argue that the special extremal slice inside an AdS black hole is dual to an absolutely maximally entangled (AME) state. We demonstrate this by confirming the $n$-independence of holographic $n$-th Renyi entropies for any bi-partite subsystems. Our result gives an AME state in an infinite-volume system, where the local bond dimension is set by the black hole entropy. In particular, our construction provides concrete support from the gravity side for the emergence of random structures and an infinite-dimensional Hilbert space in recent non-isometric holographic codes.

Sojeong Cheong, Wontae Kim

Published: 2025-08-11

Categories: gr-qc

According to the no-hair theorem, stationary black holes are uniquely characterized by their mass, charge, and angular momentum. In this paper, we explore quantum hair by deriving the quantum-corrected black hole metric within the Barvinsky-Vilkovisky formalism. The quantum-corrected metric is obtained perturbatively around flat spacetime without assuming either the commutativity between the nonlocal operator and covariant derivatives or the nonlocal Gauss-Bonnet theorem, both of which are adopted in previous studies. Using this metric, we evaluate the deflection angle in the strong-field limit and compute the associated strong gravitational lensing observables, such as the angular separation and the relative magnification. Our results show that as the quantum hair, determined by the number of virtual massless quantum fields in the nonlocal effective action, increases, the photon sphere radius, the strong deflection angle, and the relative magnification all increase, whereas the angular separation decreases. In addition, the role of quantum hair is discussed in the weak and strong naked singularities. As a result, we demonstrate that the quantum hair affects not only the black hole geometry but also its strong gravitational lensing effects.

Shin'ichi Nojiri, Sergei D. Odintsov

Published: 2025-08-11

Categories: gr-qc

We construct and investigate the dynamical black hole spacetime embedded in the expanding universe filled with cosmic fluid, such as dark energy. When the equation of state (EoS) parameter of the fluid is a constant, we find exact solutions of the Einstein equation where the Schwarzschild black hole is embedded in the expanding universe. This solution differs from the well-known McVittie metric, where the EoS parameter is not a constant but rather depends on the radial coordinate. It is shown that a dynamical black hole grows with the expansion of the universe. If primordial black holes are created before or during inflation, above dynamical black holes might be the origin of the supermassive black holes at the centre of galaxies, massive black holes suggested by the GW231123 event, and also the dark matter. The case where the cosmic fluid EoS is more general is also considered so that the universe enters the epoch of finite-time future singularity. Thermodynamics and the behaviour of black holes around different future singularities are carefully investigated. It is then demonstrated that the black hole horizon enhances the tidal force, but near the horizon, the tidal force works to press the extended object, which is in contrast with a massive body near to future singularity. We also propose a new type of future singularity where the singularity inside the black hole is a sphere with a finite radius. When the radius of the spherical singularity becomes larger than the radius of the black hole horizon, it becomes naked. The universe may end up with a cosmic doomsday when the radius of the singularity becomes infinite.

Públio Rwany B. R. do Vale

Published: 2025-08-10

Categories: gr-qc

At the quantum level, the polynomial models of gravity with six and eight derivatives are superrenormalizable, but suffer from higher derivative ghost and/or tachyonic ghost states. On the other hand, these models may have advantages in the control of negative effects of ghosts, compared to the more common fourth-derivative theory. We explore the positiveness of energy of the individual plane wave solutions in the general models with six and eight derivatives. Different from the fourth-order gravity, the part of the energy which may be seen as the leading one in the UV, is positively defined in the tensor sector. We extend this investigation to the scalar sectors of the free theory.

Noah M. MacKay

Published: 2025-08-10

Categories: gr-qc

A recent study modeled coalescing compact binaries as a spinning and contracting mass shell geometry, reinterpreting the effective one-body model. Besides obtaining the respective waveform profiles that include rates of change in binary separation and orbital frequency, an expression for the mass-shell surface energy was derived to compute the anticipated energy radiated as gravitational waves. In this study, we revisit the surface energy derivation using a variational method that was recently used, and we recover the energy's dependence on the compact binary's reduced mass, symmetric mass ratio, and the normalized rotational speed at merger. For 31 out of 93 cataloged GW events within the O1, O2 and O3 observation runs, we compute the anticipated energy radiated as gravitational waves and compare these values with the observed energy, either directly measured or extracted from the total-minus-remnant mass difference. It is shown that the model presented in this work agrees well with observed energy measurements, within the error range and via 1:1 ratios spanning from $0.828$ to $0.997$ across 29 example events (the mean value of these 29 ratios being $0.941$), with GW190403_051519 serving as an outlier with the 1:1 ratio of $0.462$, demonstrating the precision and universality of the energy expression to be applied to current and future detections.

Diganta Das, Shreyas Revankar

Published: 2025-08-10

Categories: astro-ph.CO

The combined Planck, BICEP/Keck Array and BAO measurements of the scalar spectral index and the tensor-to-scalar ratio from the cosmic microwave background observations severely constrain or completely rule out several models of inflationary potentials. On the other hand, the data seems to favor concave potentials over convex ones. In this paper, we study preheating and gravitational waves after inflation in a large-field, regularized hilltop potential where inflation takes place in the concave plateau. The inflaton, $\phi$, is coupled to a subdominant scalar field, $\chi$, through a quartic coupling. After inflation ends, $\phi$ oscillates about the potential minimum and becomes inhomogeneous. The growth of the fluctuation modes, $\delta\phi_k$ and $\delta\chi_k$, in a homogeneous, oscillating background is analyzed in linear perturbation theory, revealing that small modes likely experience broad self-resonance or external parametric resonance. To determine if the resonances are sufficiently strong to cause unstable growth of the modes we perform a lattice simulation. The lattice simulations demonstrate that, although the initial inhomogeneities generate a stochastic gravitational wave background that remains below the present observational limit, the fluctuations do not grow exponentially, and the occupation numbers of $\delta\phi_k$ and $\delta\chi_k$ remain close to zero.

Faizuddin Ahmed, Saeed Noori Gashti, Abdelmalek Bouzenada, Behnam Pourhassan

Published: 2025-08-10

Categories: gr-qc

In this study, we explore a Schwarzschild-anti de-Sitter black hole (BH) coupled with a cloud of strings (CoS) possessing both electric- and magnetic-like components of the string bivector, embedded in a Kiselev-type quintessence fluid (QF). We analyze the dynamics of photons and test particles, focusing on trajectories, photon spheres, BH shadows, and innermost stable circular orbits (ISCO), highlighting how CoS and QF parameters affect these features. We then examine the thermodynamic topology of the system by analyzing vector field zeros, showing that varying CoS leads to distinct topological configurations with total charges of either $0$ or $+1$, corresponding to known classes like RN and AdS-RN. Additionally, we study scalar field dynamics via the massless Klein-Gordon equation, reformulated into a Schr$\ddot{o}$dinger-like form to derive the effective potential. We compute the quasinormal modes (QNMs) of scalar perturbations, showing how CoS and QF influence oscillation frequencies and damping rates, with implications for gravitational confinement and thermalization in the AdS/CFT context.

Chen-Yu Yang, Ke-Jian He, Xiao-Xiong Zeng, Li-Fang Li

Published: 2025-08-10

Categories: gr-qc

This paper investigates the shadow images of rotating charged black holes in Kalb-Ramond (KR) gravity, using an accretion disk that is both optically and geometrically thin and located on the equatorial plane as the light source model. The results show that, compared to Sgr A*, the observational data of M87* impose stronger constraints on the charge parameter Q and the Lorentz-violating parameter G. Under the thin accretion disk model, a larger observer inclination theta_o deforms the inner shadow into a hat-like structure. The parameters (a, Q, G) mainly affect the size of the inner shadow and the brightness of the critical curve, where increasing these parameters reduces the shadow size and enhances the distinguishability of the critical curve. In the retrograde accretion disk case, the gravitational redshift significantly reduces the observed brightness of the image. In addition, we compute the distribution of the redshift factor on the projection screen. The results indicate that the Doppler effect induced by large theta_o enhances the blueshift in the image, while the light emitted by particles plunging into the black hole leads to strong redshift near the inner shadow. Finally, we study the polarization images under synchrotron radiation and find that the polarization intensity P_o reaches its maximum around the lensed image and higher-order images, whereas no polarization vectors appear within the inner shadow. This stands in sharp contrast to horizonless compact objects. These findings contribute to a deeper understanding of the shadow properties of charged black holes within Lorentz-violating gravity.

Kimihiro Nomura, Hidetoshi Omiya, Takahiro Tanaka

Published: 2025-08-10

Categories: astro-ph.CO

We investigate observational signatures of ultralight vector dark matter with masses $m \sim 10^{-24}$-$10^{-22}$ eV in pulsar timing arrays, taking into account general polarization states of the vector field. We find that vector dark matter induces pulsar timing residuals with nontrivial directional dependence, reflecting the anisotropic property and polarization structure specific to vector dark matter, unlike scalar dark matter. We also derive angular correlation curves of the timing residuals. Intriguingly, circular polarization of the vector dark matter enhances the quadrupole nature of the correlation curve, resulting in a more notable bending of the Hellings-Downs curve. The derived correlation curves offer a useful means to distinguish gravitational wave and dark matter contributions and to probe the nature of dark matter.

Thiago Guerreiro

Published: 2025-08-10

Categories: gr-qc

Is gravity quantum mechanical? If so, we argue that nonlinear effects in black hole ringdowns - notably second harmonic generation - generates gravitational waves in non-classical states. While quantum features of these states such as sub-Poissonian statistics or entanglement could in principle be measured at interferometric detectors, the tiny coupling of gravity to matter makes this extremely challenging. Drawing on ideas from quantum optics, we instead propose that the nonlinearities in ringdowns could be used as strongly coupled detectors of quantum gravitational radiation, potentially offering a new route to probing the quantum nature of gravity.

Maciej T. Jarema, Cameron R. D. Bunney, Vitor S. Barroso, Mohammadamin Tajik, Chris Goodwin, Silke Weinfurtner

Published: 2025-08-10

Categories: quant-ph

Understanding quantum correlations through information-theoretic measures is fundamental to developments in quantum field theory, quantum information, and quantum many-body physics. A central feature in a plethora of systems is the area law, under which information scales with the size of the boundary of the system, rather than volume. Whilst many systems and regimes exhibiting an area law have been identified theoretically, experimental verification remains limited, particularly in continuous systems. We present a methodology for measuring mutual information in an experimental simulator of non-interacting quantum fields, and propose using the analogue $(2 + 1)$-dimensional spacetime offered by thin films of superfluid helium. We provide numerical predictions incorporating the natural thermal state of the helium sample that exemplify an area-law scaling of mutual information, and characterise deviations attributable to the inherent finite system size.

Dmitry D. Ofengeim, Tsvi Piran

Published: 2025-08-10

Categories: astro-ph.HE

The air shower array Carpet-3 detected a 300 TeV photon from the direction of GRB 221009A at 4536 s after the Fermi-GBM trigger for this event. If the association with this gamma-ray burst is real, it poses two puzzles. First, why was this photon not absorbed by the extragalactic background light? ``New physics'' beyond the Standard Model is required to explain how it managed to reach Earth from a cosmological distance. Second, why was this photon detected when the VHE afterglow observed by LHAASO already faded? A novel astrophysical mechanism is required to explain this delay. In this work we show that Lorentz invariance violation (LIV), which arises as a low-energy limit of certain quantum gravity theories, can solve both puzzles. It shifts thresholds of particle interaction and changes the opacity of the extragalactic background, and cause energy-dependent variations of the photon velocity, which changes the photon time of flight. We investigate the LIV parameter space assuming that the 300 TeV photon is a part of the VHE afterglow detected by LHAASO in the TeV range. We identify viable solutions and place stringent two-sided constraints on the LIV energy scale required to resolve the observational puzzles. First-order LIV appears to be incompatible with the constraints set by analyzing the TeV afterglow of this GRB. Viable solutions emerge for higher orders. In particular, the commonly studied second-order subluminal LIV with $E_{\rm LIV2} = 1.30_{-0.35}^{+0.56} \times 10^{-7} E_{\rm Pl}$ (95.4% credibility level; $E_{\rm Pl}$ is the Planck energy) is consistent with all the observed data.

Rongrong Zhai, Chengjie Fu, Xiangyun Fu, Puxun Wu, Hongwei Yu

Published: 2025-08-09

Categories: astro-ph.CO

In this paper, we investigate the inflationary phenomenology of parity-violating (PV) extensions of symmetric teleparallel gravity by applying this PV gravity theory to axion inflation. The presence of PV terms induces velocity birefringence in the tensor perturbations. During inflation, when the inflaton rapidly traverses the cliff-like region in its potential, the tensor modes at specific scales for one of the two circular polarization states undergo significant amplification due to tachyonic instability. Consequently, the resulting primordial gravitational waves (GWs), characterized by a one-handed polarization and a multi-peak structure in their energy spectrum, exhibit a significant amplitude potentially detectable by LISA and Taiji, and their chirality could be determined by the LISA-Taiji network. The detection of such a chiral GW signal provides an opportunity to probe inflation and PV gravity theory.

Parthapratim Mahapatra, Sayantani Datta, Ish Gupta, Poulami Dutta Roy, Muhammed Saleem, Purnima Narayan, Soumen Roy, Jan Steinhoff, Deirdre Shoemaker, Alan J. Weinstein, Anuradha Gupta, B. S. Sathyaprakash, K. G. Arun

Published: 2025-08-09

Categories: gr-qc

We present a comprehensive assessment of multiparameter tests of general relativity (GR) in the inspiral regime of compact binary coalescences using Principal Component Analysis (PCA). Our analysis is based on an extensive set of simulated gravitational wave signals, including both general relativistic and non-GR sources, injected into zero-noise data colored by the noise power spectral densities of the LIGO and Virgo detectors at their designed sensitivities. We evaluate the performance of PCA-based methods in the context of two established frameworks: TIGER and FTI. For GR-consistent signals, we find that PCA enables stringent constraints on potential deviations from GR, even in the presence of multiple free parameters. Applying the method to simulated signals that explicitly violate GR, we demonstrate that PCA is effective at identifying such deviations. We further test the method using numerical relativity waveforms of eccentric binary black hole systems and show that missing physical effects-such as orbital eccentricity-can lead to apparent violations of GR if not properly included in the waveform models used for analysis. Finally, we apply our PCA-based test to selected real gravitational-wave events from GWTC-3, including GW190814 and GW190412. We present joint constraints from selected binary black hole events in GWTC-3, finding that the 90% credible bound on the most informative PCA parameter is $0.03^{+0.08}_{-0.08}$ in the TIGER framework and $-0.01^{+0.05}_{-0.04}$ in the FTI framework, both of which are consistent with GR. These results highlight the sensitivity and robustness of the PCA-based approach and demonstrate its readiness for application to future observational data from the fourth observing runs of LIGO, Virgo, and KAGRA.

A. Kazım Çamlıbel, M. Akif Feyizoğlu, İbrahim Semiz

Published: 2025-08-09

Categories: gr-qc

In this work, we revisit/reinterpret/extend the model-independent analysis method (which we now call spread - luminosity distance fitting, spread-LDF) from our previous work. We apply it to the updated supernova type Ia catalogue, Pantheon+ and recent GRB compilations. The procedure allows us, using only FLRW assumption, to construct good approximations for expansion history of the universe, re-confirming its acceleration to be a robust feature. When we also assume General Relativity ("GR"), we can demonstrate, without any matter/energy model in mind, the need for (possibly nonconstant) dark energy ("GDE"). We find hints for positive pressure of GDE at z>1 with implications on either the complexity of dark energy, or the validity of one of the cosmological principle, interpretation of SN Ia data, or GR.

Brett McInnes

Published: 2025-08-09

Categories: gr-qc

There have been persistent suggestions, based on several diverse data sets, that the cosmic expansion is not exactly isotropic. It is not easy to develop a coherent theoretical account of such a ``Hubble anisotropy'', for, in standard General Relativity, intuition suggests that it contradicts the predictions of the very successful Inflationary hypothesis. We put this intuition on a firm basis, by proving that if we [a] make use of an Inflationary theory in which Inflation isotropises spatial geometry -- $\,$ this, of course, includes the vast majority of such theories -- $\,$ and if [b] we insist on assuming that spacetime has a strictly metric geometry (one in which the geometry is completely determined by a metric tensor), then indeed all aspects of the ``Hubble field'' must be isotropic. Conversely, should a Hubble anisotropy be confirmed, then either we must contrive to build anisotropy into Inflation from the outset, or we will have to accept that spacetime geometry is not strictly metric. We argue that allowing spacetime torsion to be non-zero would be by far the most natural way to accommodate such observations. Such theories make firm predictions, as for example that there should be a correlation between the degree of anisotropy at the end of Inflation and a certain specific component of the Hubble tension.

Erdem Sucu, Suat Dengiz, İzzet Sakallı

Published: 2025-08-08

Categories: gr-qc

We explore the thermodynamic and optical properties of Einstein-Dyonic-ModMax (EDM) black holes (BHs) incorporating quantum gravity corrections and plasma effects. The ModMax theory promotes the classical Maxwell theory to a non-linear electrodynamics with a larger symmetry structure (electromagnetic duality plus conformal invariance), and provides dyonic BH solutions characterized by both electric and magnetic charges modulated by the nonlinearity parameter $\gamma$. Using the Hamilton-Jacobi tunneling formalism, we derive the Hawking radiation spectrum and demonstrate how the Generalized Uncertainty Principle (GUP) modifies the thermal emission, potentially leading to stable remnants. Our analysis of gravitational lensing employs the Gauss-Bonnet theorem to compute light deflection angles in both vacuum and plasma environments, revealing strong dependencies on the ModMax parameter and plasma density. We extend this to axion-plasmon environments, uncovering frequency-dependent modifications that could serve as dark matter signatures. The photon motion analysis in plasma media shows how the exponential damping term $e^{-\gamma}$ affects electromagnetic backreaction on spacetime geometry. We compute quantum-corrected thermodynamic quantities, including internal energy, Helmholtz free energy, pressure, and heat capacity, using exponentially modified entropy models. The heat capacity exhibits second-order phase transitions with critical points shifting as functions of $\gamma$, indicating rich thermodynamic phase structures. Energy condition analysis reveals violations in near-horizon regions, characteristic of exotic matter supporting these geometries.

Federico Armato, Barbara Garaventa, Andrea Chincarini

Published: 2025-08-08

Categories: physics.ins-det

The Einstein Telescope is the next-generation gravitational wave interferometer which, compared to current detectors, will enable the observation of gravitational signals at lower frequencies with a sensitivity improved by approximately two orders of magnitude. Achieving such exceptional sensitivity requires minimizing all sources of noise. In the low-frequency regime, magnetic noise is one of the dominant. This article examines the effectiveness and limitations of a passive mitigation technique: ferromagnetic shielding.

Peter Hintz, Oliver Petersen, András Vasy

Published: 2025-08-08

Categories: gr-qc

We show the stability of Kerr-de Sitter black holes, in the full subextremal range, as solutions of the vacuum Einstein equation with a positive cosmological constant under the assumption that mode stability holds for these spacetimes. The method is similar to the (unconditional) proof in the slowly rotating case by Hintz and Vasy. The key novelties are the implementation of constraint damping in the full subextremal range as well as the verification of a subprincipal symbol condition at the trapped set.

Harshal Kulkarni, Romain Ruzziconi, Akshay Yelleshpur Srikant

Published: 2025-08-08

Categories: hep-th

Carrollian holography is a framework for flat space holography, suggesting that gravity in asymptotically flat spacetime in $D$ dimensions is dual to a conformal Carrollian field theory in $D - 1$ dimensions living at null infinity. In this work, we elaborate on the definition of Carrollian amplitudes for massless scalar fields in general dimensions and provide explicit expressions for the two-, three-, and four-point functions. We show that these amplitudes naturally arise from Lorentzian holographic correlators in AdS/CFT through a correspondence between the flat space limit in the bulk and the Carrollian limit at the boundary. Finally, we use the relation between Carrollian and celestial holography to derive explicit expressions for celestial amplitudes in $D$ dimensions, which are reinterpreted as correlators of the celestial CFT in $D - 2$ dimensions.

Andrés Boasso, Francisco D. Mazzitelli

Published: 2025-08-08

Categories: hep-th

We compute the renormalized stress-energy tensor for a massless quantum scalar field in the background of the horizonless Bardeen spacetime. Within the weak-field approximation, we show that the vacuum fluctuations differ significantly between conformally and non-conformally coupled fields, both in magnitude and in their behavior at short and intermediate distances. At large distances, we recover the universal asymptotic behavior previously observed in black hole and Newtonian star backgrounds. Going beyond the weak-field regime, we find that, for certain parameter ranges, the modes of the field can develop imaginary frequencies, leading to instabilities and an exponential growth of vacuum fluctuations. We also discuss critically the applicability of the anomaly-induced effective action for computing the renormalized stress-energy tensor in the conformally coupled case.

Andrei O. Barvinsky, Alexey E. Kalugin, Władysław Wachowski

Published: 2025-08-08

Categories: hep-th

We suggest a systematic calculational scheme for heat kernels of covariant nonminimal operators in causal theories whose characteristic surfaces are null with respect to a generic metric. The calculational formalism is based on a pseudodifferential operator calculus which allows one to build a linear operator map from the heat kernel of the minimal operator to the nonminimal one. This map is realized as a local expansion in powers of spacetime curvature, dimensional background fields, and their covariant derivatives with the coefficients -- the functions of the Synge world function and its derivatives. Finiteness of these functions, determined by multiple proper time integrals, is achieved by a special subtraction procedure which is an important part of the calculational scheme. We illustrate this technique on the examples of the vector Proca model and the vector field operator with a nondegenerate principal symbol. We also discuss smoothness properties of heat kernels of nonminimal operators in connection with the nondegenerate nature of their operator symbols.

P. Pnigouras, N. Andersson, F. Gittins, A. R. Counsell

Published: 2025-08-08

Categories: gr-qc

Motivated by future opportunities in gravitational-wave astronomy and the ongoing effort to constrain physics under extreme conditions, we consider the signature of individual mode resonances excited during the inspiral of binary systems involving neutron stars. Specifically, we quantify how each resonant mode contributes to the effective (frequency-dependent) tidal deformability. The resonant solution is shown to be accurately represented by a new closed-form approximation, which sheds light on the involved phenomenology, and which should be useful for the development of precise waveform models and future parameter extraction efforts.

Rahime Matur, Ian Hawke, Nils Andersson

Published: 2025-08-08

Categories: astro-ph.HE

The recent detection of GW230529 suggests that black hole-neutron star mergers may involve low-mass black holes, potentially producing detectable electromagnetic counterparts. Motivated by this, we perform eleven fully general-relativistic hydrodynamic simulations with and without neutrino treatment, targeting the inferred chirp mass of GW230529. We systematically vary the black hole spin from $a_{\mathrm{BH}} = 0.0$ to $0.8$ in steps of $0.1$, making this the most comprehensive study of spin effects in black hole-neutron star mergers to date. We confirm our earlier findings of fast-moving ejecta ($v \geq 0.6\,c$) in this parameter regime and demonstrate a clear spin dependence, with fast-ejecta masses reaching up to $\qty{\sim e-3}{\Mass\Sun}$ for $a_{\mathrm{BH}} = 0.8$. Most notably, we identify for the first time the presence of spiral wave-driven ejecta in black hole-neutron star mergers -- a phenomenon previously reported only in binary neutron star systems. The mass of this component grows significantly with spin, reaching levels up to $\qty{\sim 7e-3}{\Mass\Sun}$. These results establish a new spin-enhanced mechanism for powering blue kilonova emission in black hole-neutron star mergers, significantly extending the range of systems expected to produce observable electromagnetic counterparts.

Alexandre Landry, Yassine Sekhmani, Emmanuel N. Saridakis, Sunil K Maurya, Akram Ali

Published: 2025-08-08

Categories: gr-qc

In this paper, we derive a novel class of exact, static, spherically symmetric traversable wormhole solutions in teleparallel $F(T)$ gravity augmented by the non-linear de Rham-Gabadadze-Tolley (dRGT) graviton mass term. By using the Morris-Thorne ansatz with a generalized redshift function including constant, logarithmic, and power-law profiles, we rigorously integrate the dRGT-modified conservation laws together with the teleparallel field equations to reconstruct both the shape function $b(r)$ and the possible torsion-based teleparallel $F(T)$ solutions. Our solutions, which accommodate both pressureless dust and dark-energy perfect fluids, are naturally expressed via special function representations. We verify the flaring-out condition $b'(r_0)<1$, demonstrate the absence of event horizons, and show that the null and weak energy conditions are either strictly satisfied or incur only controlled violations at the throat. These results establish teleparallel massive gravity as a self-consistent, mathematically rich framework for asymptotically flat wormhole geometries without necessarily invoking an explicit cosmological constant.

Erik Amorim

Published: 2025-08-08

Categories: gr-qc

We establish the existence of a family of static, spherically symmetric spacetimes that are solutions of the Einstein Field Equations of General Relativity coupled to the electric field of a static point charge obeying the equations of electromagnetism of Maxwell-Bopp-Land\'e-Thomas-Podolsky. The point charge is modeled as a naked singularity with non-positive bare mass. The singularity at the location of the charge is milder than that of the Reissner-Weyl-Nordstr\"om solution to the conventional Einstein-Maxwell equations, and, contrary to what happens for the latter, the electric-field energy of these solutions is finite.

Rajes Ghosh, R. Prasad, Kabir Chakravarti, Prayush Kumar

Published: 2025-08-08

Categories: gr-qc

Observations of astrophysical binaries may reveal departures from pure Keplerian orbits due to environmental influences, modifications to the underlying gravitational dynamics, or signatures of new physics. In this work, we develop a unified framework to systematically study such perturbations in the ambit of perturbed Kepler problem, and explore their impact on eccentric orbital dynamics and gravitational wave emission. Unlike traditional parametrized frameworks such as post-Newtonian and post-Einsteinian expansions, our approach offers a more source-specific modeling strategy, making it more natural to trace the physical origins of various model parameters. Starting from a general perturbed potential, we derive the modified orbit and compute the associated gravitational fluxes and phase evolution, assessing their observational relevance for both current and future detectors. This framework thus offers a general and physically transparent toolkit to probe such subtle effects in gravitational wave data.

Kratika Mazde, Lisa Mickel, Patrick Peter

Published: 2025-08-08

Categories: gr-qc

Predictions from early universe cosmology typically concern primordial perturbations generated during epochs where effects arising from the quantum nature of gravity may be important; quantum vacuum fluctuations being stretched to cosmological scales during a phase of inflation. Quantizing the background is then done by assuming a single close-to-classical state over which perturbations grow, as well as a Born-Oppenheimer factorization throughout the relevant phase. We present a scenario in which although the latter factorization remains valid at all times, we allow the background state to be very non-classical by defining quantum trajectories through an eikonal approximation. We find that these trajectories asymptotically reproduce an almost classical behavior for the background, but the predictions for the power spectrum of perturbations can significantly differ.

Aritra Sanyal, Praveen Kumar Dhankar, Albert Munyeshyaka, Safiqul Islam, Farook Rahaman

Published: 2025-08-08

Categories: gr-qc

We study the emergence of cosmic hysteresis in cyclic bouncing universes within the framework of analytically reconstructed $f(R)$ gravity. Using exact bouncing scale factor solutions of exponential and power-law forms, we reconstruct the corresponding $f(R)$ models and investigate the thermodynamic behavior of a minimally coupled scalar field in these geometries. The pressure evolution during expansion and contraction phases is shown to be asymmetric, leading to a non-vanishing thermodynamic work integral over each cycle, defined by $\oint p_\phi\, dV$. We identify closed hysteresis loops in the equation-of-state space and quantify the net energy transfer per cycle. Our results reveal that such reconstructed $f(R)$ models generically support irreversible evolution, demonstrating a natural emergence of the thermodynamic arrow of time. These findings provide new insight into the dissipative features of modified gravity and the long-term dynamics of cyclic cosmological scenarios.

Giovanni Amelino-Camelia, Giuseppe Fabiano, Domenico Frattulillo, Flavio Mercati

Published: 2025-08-08

Categories: gr-qc

IR/UV mixing (a mechanism causing ultraviolet quantum-gravity effects to manifest themselves also in a far-infrared regime) is a rare case of feature found in several approaches to the quantum-gravity problem. We here derive the implications for "soft" IR/UV mixing (corrections to the dispersion relation that are linear in momentum) of some recent cold-atom-interferometry measurements. For both signs of the IR/UV-mixing correction term we establish bounds on the characteristic length scale which reach the Planck-length milestone. Intriguingly, for values of the characteristic scale of about half the Planck length we find that IR/UV mixing provides a solution for a puzzling discrepancy between Cesium-based and Rubidium-based atom-interferometric measurements of the fine structure constant.

Marek Rogatko

Published: 2025-08-08

Categories: gr-qc

In our paper we pay attention to the problem of uniqueness (classification) of higher-dimensional electro-magnetic static, asymptotically flat, non-extremal solutions of multi-dimensional Einstein (n-2)-form gauge field gravity theory, which possess a photon sphere. The photon sphere is uniquely described by its asymptotic data. Conformal positive energy theorem is the key tool in the proof.

Muhammed Saleem, Hsin-Yu Chen, Daniel M. Siegel, Philippe Landry, Jocelyn S. Read, Kaile Wang

Published: 2025-08-08

Categories: astro-ph.HE

Since the discovery of the binary neutron star merger GW170817 and its associated kilonova, neutron star mergers have been established as a key production channel for $r$-process elements in the Universe. However, observations of $r$-process abundances as inferred from stellar spectra of Milky Way disk stars, together with chemical evolution modeling, suggest that additional channels are needed to fully account for the $r$-process element enrichment in the Milky Way. Neutron star-black hole mergers and fast-merging binary neutron star systems are among the leading alternative candidates. In this study, we combine gravitational-wave observations from LIGO-Virgo-KAGRA with data from short gamma-ray bursts, Galactic pulsars, and Galactic [Eu/Fe] vs [Fe/H] abundance observations to assess the contribution of these mergers to $r$-process enrichment in the Galactic disk. We find that neither neutron star-black hole mergers nor fast-merging binary neutron star populations can serve as the dominant additional channel without generating strong tension with existing observations and theoretical expectations. These results constrain the viable sources of Galactic $r$-process enrichment and underscore the necessity of non-merger production channels.

M. Sharif, M. Zeeshan Gul, Ahmad Nawaz

Published: 2025-08-08

Categories: gr-qc

The primary aim of this work is to explore feasible bouncing cosmological solutions in the framework of $f(\mathcal{Q}, \mathcal{C})$ gravity, where $\mathcal{Q}$ denotes non-metricity and $\mathcal{C}$ indicates the boundary term. To achieve this, we analyze the dynamics of a Bianchi type-I spacetime with perfect fluid distribution. We consider various functional forms of $f(\mathcal{Q,C})$ theory to assess how this modified gravity framework influences cosmic evolution. Additionally, we examine the dynamics of different cosmological parameters to explore non-singular bounce solutions. We also use linear perturbation to study the stability analysis. Our findings reveal the breach of the null energy conditions, which is required for the existence of viable bounce solutions. The equation of state parameter demonstrates either a quintessence phase or a phantom regime of the universe, demonstrating that the cosmos is undergoing accelerating expansion. This gravitational framework presents a promising alternative to the standard cosmological model, presenting an innovative viewpoint on gravitational interactions and the dynamics of the early universe.

Richard Lieu

Published: 2025-08-08

Categories: astro-ph.HE

By assuming the inverse square law of solar wind plasma density as representative of other stars, it is shown that just outside a star the {\it outward} deflection of a passing radio signal at $\nu\approx 1$~GHz (which is capable of penetrating the plasma) is about 5 times larger than the gravitational inward deflection by the star, and the ensuing lens equation which takes both effects into account is a cubic polynomial with three roots and a new strong lensing caustic. The geometric optics approach is valid for a radio source size $\lesssim 1$~pc. Microlensing magnification of a steady background source occurs typically over a timescale of milliseconds, resulting in $\approx 80$ Fast Radio Bursts (FRBs) per day over the whole sky, which can only perturb the isotropy of FRB distribution at the several \% level. Moreover, repeating FRBs could be triggered by the periodic interception of the line-of-sight of the background source by members of a binary system. The temporal signatures of such FRBs are consistent with the power spectrum of solar wind density fluctuations on corresponding scales, except the mean density of the wind is a few times higher than the solar value.

Eduardo A. B. Oliveira, Andre G. S. Landulfo

Published: 2025-08-07

Categories: gr-qc

It is expected that a quantum theory of gravity will radically alter our current notion of spacetime geometry. However, contrary to what was commonly assumed for many decades, quantum gravity effects could manifest in scales much larger than the Planck Scale, provided that there is enough coherence in the superposition of geometries. Quantum Clocks, i.e. quantum mechanical systems whose internal dynamics can keep track of proper-time lapses, are a very promising tool for probing such low-energy quantum gravity effects. In this work, we contribute to this subject by proposing a spacetime-covariant formalism to describe clocks in first quantization. In particular, we account for the possibility of dynamically accelerated clocks via suitable couplings with external fields. We find that a particular decomposition of the (quadratic) clock Hamiltonian into positive- and negative-mass sectors, when attainable, enables one to compute the evolution of the system directly in terms of the clock's proper-time while maintaining explicit covariance. When this decomposition is possible, the evolution obtained is always unitary, even with couplings with external fields used to, e.g., accelerate the clocks. We then apply this formulation to compute the joint time evolution of a pair of quantum clocks in two cases: (i) inertial clocks with relative motion and (ii) charged clocks accelerated by a uniform magnetic field. In both cases, when our clocks are prepared in coherent states, we find that the density matrix $\rho_{\tau_2|\tau_1}$ describing time-measurements of the two clocks yields not only conditional probabilities whose peaks match exactly the classical expected values for time dilation, but also yields coherent quantum fluctuations around that peak with a Gaussian profile.

Partha Nandi, Frederik G. Scholtz

Published: 2025-08-07

Categories: hep-th

We investigate how low-frequency gravitational waves (LFGWs), originating from distant astrophysical or cosmological sources, can induce purely quantum geometric phases in mesoscopic optomechanical systems. These phases represent subtle imprints with no classical counterpart, going beyond standard dynamical or Berry-type contributions that admit Hannay-angle analogues. Such ultra-weak waves couple to the motion of a mechanical mirror and generate distinctive phase shifts in the system's quantum state that cannot arise in any classical description. To access this effect, we propose a Ramsey-type interferometric protocol in which the photon-number states of a quantized optical mode become entangled with the mirror's center-of-mass motion, enabling a direct readout of the LFGW-induced geometric phase. This framework establishes a distinctly quantum approach for probing low-frequency gravitational wave modes, offering an alternative to conventional detection strategies based on spacetime strain.

Grigorios Papigkiotis, Georgios Vardakas, Nikolaos Stergioulas

Published: 2025-08-07

Categories: astro-ph.HE

Relations between stellar properties independent of the nuclear equation of state offer profound insights into neutron star physics and have practical applications in data analysis. Commonly, these relations are derived from utilizing various realistic nuclear cold hadronic, hyperonic, and hybrid EoS models, each of which should obey the current constraints and cover a wide range of stiffnesses. Concurrently, the field of multimessenger astronomy has been significantly enhanced by the advent of gravitational wave astronomy, which increasingly incorporates deep learning techniques and algorithms. At the same time, X-ray spectral data from NICER based on known pulsars are available, and additional observations are expected from upcoming missions. In this study, we revisit established universal relations, introduce new ones, and reassess them using a feed-forward neural network as a regression model. More specifically, we mainly propose ``deep'' EoS-insensitive hypersurface relations for rapidly rotating compact objects between several of the star's global parameters, which achieve an accuracy of within $1\%$ in most cases, with only a small fraction of investigated models exceeding this threshold. While analytical expressions can be used to represent some of these relations, the neural network approach demonstrates superior performance, particularly in complex regions of the parameter space. Furthermore, we use the SHapley Additive exPlanations (SHAP) method to interpret the suggested network's predictions, since is based on a strong theoretical framework inspired by the field of cooperative Game Theory. Most importantly, these highly accurate universal relations empowered with the interpretability description could be used in efforts to constrain the high-density equation of state in neutron stars, with the potential to enhance our understanding as new observables emerge.

Cheng Ran, Shao-Feng Wu, Zhuo-Yu Xian

Published: 2025-08-07

Categories: hep-th

We present a data-driven method for holographic bulk reconstruction that works even when the spacetime is not asymptotically AdS. Given the data of boundary Green functions within a finite frequency window, we iteratively adjust a bulk metric with a finite radial cutoff until its holographic Green functions reproduce the boundary data. Based on the holographic Wilsonian renormalization group for the Klein-Gordon equation in an undetermined curve space, we construct a radial flow equation and transform it into a Neural ODE, which is an infinite-depth neural network for modeling continuous dynamics. Assuming the double-trace coupling $h$ in the Wilsonian action is real, we demonstrate that the Neural ODE can effectively learn the metrics with AdS, Lifshitz, and hyperscaling violated asymptotics. In particular, we apply the algorithm to the Sachdev-Ye-Kitaev (SYK) model which slightly deviates from the conformal limit. In the hyperparameter space spanned by the rescaled temperature $\bar{T}$ and the radial cutoff $\epsilon$, we identify a critical curve along which the learned metric is close to AdS$_2$ black hole with finite cutoff. We derive an approximate analytical expression for this curve, from which an effective bulk dual of the SYK coupling $v$ is established. Our work provides a promising way for using machine learning to depict the novel bulk geometry dual to the non-conformal boundary systems in the real world.