General Relativity and Quantum Cosmology
Black Holes, Gravitational Waves and Space-Time Singularities Lemaitre Conference 2024
Massimo Bianchi, Sergio Luigi Cacciatori, Matteo Galaverni et al. (+2 more)
This editorial introduces the topical collection arising from the Lemaitre Conference 2024 - the second in a series of meetings dedicated to the scientific legacy of Georges Lemaitre - held at the Vatican Observatory in Castel Gandolfo, 17-20 June 2024, fifty-seven years after Lemaitre's death and on the eve of the centenary of his foundational 1927 paper on the expanding universe. The nineteen contributions collected here address the most pressing open problems at the interface of cosmology, gravitation, and
quantum theory: the Hubble tension and the future of ${\Lambda}$CDM in light of recent DESI data; inflationary cosmology and dark-energy model-building in string theory and supergravity, together with the Swampland constraints that bound them; the observer-dependence of the
quantum-cosmological wave function; the removal, or consistent crossing, of spacetime singularities - from the canonical quantization of Lemaitre's own 1933 dust model to string-theoretic pre-Big-Bang bounces and many-body constructions of singularity-free black-hole cores; primordial black holes and their gravitational-wave signatures; the search for a background-independent formulation of
quantum gravity and a first-principles account of horizon thermodynamics; and the foundational status of the
quantum-to-classical transition in gravitational contexts. A proposal for lunar-based cosmological observations, and a historical reconstruction of the genesis of Lemaitre's primeval-atom hypothesis, complete the collection. A recurring unifying thread was the legacy of Lemaitre himself - who first distinguished coordinate from physical singularities and coined the term "horizon" - whose pioneering
vision continues to guide research at the frontier of cosmology and fundamental physics.
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All authors Massimo Bianchi, Sergio Luigi Cacciatori, Matteo Galaverni, Gabriele Gionti, Fabio Scardigli
General Relativity and Quantum Cosmology · Cross-listed from astro-ph.CO
Interacting fluid cosmologies from the metric-affine framework
Fotios K. Anagnostopoulos and Damianos Iosifidis
Metric-affine
gravity provides a natural
geometric framework in which spacetime
curvature, torsion, and non-metricity are treated as independent degrees of freedom, leading to novel cosmological dynamics beyond General Relativity. A generic consequence of such theories is the emergence of effective interactions among the cosmological fluids, even in the absence of explicit phenomenological couplings. Interestingly, the above happens while the Standard Model of Particle physics remains unmodified. In this work, we investigate interacting cosmological models that arise from metric-affine
gravity and analyze their implications for the background
evolution of the Universe. We derive the modified continuity equations governing the matter, radiation, and dark-energy components, highlighting the
geometric origin of energy exchange in the dark sector. We discuss how these interactions modify the expansion history and can effectively mimic evolving dark-energy behavior. The resulting cosmological scenarios are confronted with the most recent observational data from Type Ia
Supernovae (Pantheon+),
Cosmic Chronometers, and Baryon Acoustic Oscillations (DESI DR2). Moreover, using model selection criteria, e.g., Akaike Information Criterion,
Bayesian Information Criterion and the
Bayesian Evidence, we compare the aforementioned models against the standard $\Lambda$CDM model. We find that the proposed framework performs slightly better than $\Lambda CDM$, in the light of the data sets considered here. Our analysis demonstrates that metric-affine-induced interactions constitute a viable and theoretically motivated alternative for the description of the Universe.
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General Relativity and Quantum Cosmology
Nonradial oscillations of realistic anisotropic neutron stars: Polar modes
L. M. Becerra, José F. Rodríguez-Ruiz, E.A. Becerra-Vergara et al. (+1 more)
In this work, we study the polar perturbations of static, spherically symmetric
neutron stars with anisotropic pressure in full general relativity, including linear-order perturbations of both the metric and the fluid. We calculate the $f$-mode frequencies and the corresponding damping times using a consistent treatment of the perturbation of the radial vector $k^\alpha$. In particular, its Lagrangian perturbation $\Delta k^\alpha$ is determined by the metric perturbations and the fluid Lagrangian displacement and is constrained to the $(\tilde{u},\tilde{k})$ plane, where $\tilde{u}^\alpha$ is the normalized fluid four-velocity. This constraint introduces an additional dynamical degree of freedom into the perturbation equations. Considering three equations of state and the Horvat and Bowers-Liang prescriptions for pressure anisotropy, we find that the $f$-mode frequency increases with stellar mass, ranging from $1$ to $3$~kHz, while the damping time decreases, ranging from $0.5$ to $1.25$~s. Increasing anisotropy, in the sense of tangential pressure exceeding radial pressure, generally lowers the oscillation frequency, while its effect on the damping time depends on the anisotropy prescription: the damping time decreases with increasing anisotropy for the Horvat model but increases with increasing anisotropy for the Bowers-Liang model. We further find quasi-universal relations between the real and imaginary parts of the $f$-mode frequency, $M\omega_R$ and $M\omega_I$, and the stellar compactness $\mathcal{C}=M/R$, which are largely insensitive to the equation of state.
Polynomial fits to these relations achieve an accuracy better than $10\%$, providing a simple phenomenological framework for constraining
neutron-
star pressure anisotropy through future asteroseismology observations.
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All authors L. M. Becerra, José F. Rodríguez-Ruiz, E.A. Becerra-Vergara, F. D. Lora-Clavijo
General Relativity and Quantum Cosmology
NRSur7dq4v2: A multi-domain precessing surrogate model with improved accuracy
Abhishek Ravishankar, Vijay Varma, Scott E. Field et al. (+5 more)
Numerical relativity simulations provide the most accurate waveforms for binary black hole coalescences, but are prohibitively expensive for direct use in gravitational-wave data analysis. Surrogate models overcome this cost, and NRSur7dq4 is commonly used in parameter estimation for this reason. However, there is evidence in the literature that NRSur7dq4's accuracy could be improved in the merger-ringdown portion of the waveform, which is particularly important for the analysis of high-mass binary black hole events. Motivated by these observations, we construct NRSur7dq4v2, a multi-domain extension of NRSur7dq4 in which overlapping temporal subdomains allow tighter, independent error control over the inspiral and merger-ringdown portions of the waveform before they are smoothly combined. To assess the new model's performance in the merger-ringdown regime, we infer the mass and
spin of the remnant black hole from quasi-normal fits to the ringdown portion of the surrogate waveform. We find that NRSur7dq4v2 produces significantly improved remnant mass and
spin estimates, with gains of roughly factors of $3$ to $10$ over NRSur7dq4. Compared to NRSur7dq4, NRSur7dq4v2 also includes modes up to $\ell=5$, includes more accurate modeling of certain subdominant modes, and introduces a runtime model-complexity feature that gives users direct control over the tradeoff between evaluation cost and accuracy. Finally, alongside the model development, we have optimized the gwsurrogate package to achieve a fourfold speedup for precessing surrogates. The resulting precessing surrogates called through gwsurrogate are now slightly faster than their LALSimulation counterparts.
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All authors Abhishek Ravishankar, Vijay Varma, Scott E. Field, Keefe Mitman, Nils Deppe, Leo C. Stein, Michael Boyle, Mark A. Scheel
General Relativity and Quantum Cosmology · Cross-listed from hep-th
Entanglement Wedge Reconstruction Beyond the Large N Limit via the Twirled Petz Map
Arash Alipour Shahmiri, Maryam Sharifian and Niloofar Vardian
Entanglement wedge reconstruction provides the sharpest formulation of bulk locality in AdS/CFT, identifying the
entanglement wedge as the largest bulk region reconstructible from a boundary subregion. While this statement is well understood at leading order in the large N expansion through both modular flow and Petz map reconstruction, its extension beyond the semiclassical regime has remained unclear. In this work, we show that
quantum error correction provides the natural framework for addressing this problem. At leading order, we reproduce the known leading-order reconstruction formulas, and by employing the twirled Petz map, we obtain a systematic and explicit method for incorporating subleading 1/N corrections. Beyond the leading approximation, we have obtained a bi-local correction controlled by a subleading Petz kernel. Our results establish a controlled approach to bulk reconstruction beyond large N and sharpening the role of
quantum error correction in holography. This framework provides a controlled path toward understanding bulk reconstruction in fully
quantum gravitational settings.
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General Relativity and Quantum Cosmology
Scalar field with nonminimal couplings to metric-affine geometry
Ilaria Andrei, Damianos Iosifidis, Laur Järv et al. (+1 more)
We study a scalar field nonminimally coupled to metric-affine
gravity within actions linear in the affine
curvature and containing all independent parity-even and parity-odd terms quadratic in torsion and nonmetricity, including mixed contractions. We also include Nieh-Yan-like derivative couplings between the scalar-field derivative and the four torsion and nonmetricity vectors. We derive the connection, metric, and scalar-field equations and, since the connection equation is algebraic, eliminate the independent connection on the generic nondegenerate branch to obtain an equivalent metric scalar-tensor theory in which the non-Riemannian interactions are encoded in an effective kinetic function. We classify several sectors and find that the pure quadratic nonmetricity and pure quadratic torsion sectors separately leave the Einstein-frame kinetic function unchanged relative to the simplest metric-affine scalar-tensor model, whereas their simultaneous presence, the derivative couplings, and generic mixed torsion-nonmetricity interactions can modify it. In the derivative-coupling sector, projective consistency imposes a relation among the couplings. We then consider
polynomial coupling functions and study the resulting canonical field redefinition and Einstein-frame potentials. In particular, we illustrate how derivative and mixed torsion–nonmetricity couplings reshape quadratic and quartic potentials in canonical-field space, and show that a quadratic Jordan-frame potential can be mapped, for a suitable choice of derivative and nonminimal couplings, into a natural-inflation potential after canonical normalization. Finally, we separately impose the cosmological principle, determine the reduced combinations of quadratic couplings and the scalar field hypermomentum, and obtain the corresponding modified cosmological equations in the simplest sectors.
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All authors Ilaria Andrei, Damianos Iosifidis, Laur Järv, Margus Saal
General Relativity and Quantum Cosmology
Coherent Selection of Critical Kasner Response
Yi-kun Li
A coherent wave component with extremely small initial self-energy can substantially change the first response of a contracting spacetime. We demonstrate this effect in Einstein–Maxwell–scalar theory with two commuting spacelike Killing fields. Along a critical family motivated by scalarized black-hole interiors, the estimated
magnetic delay leaves time for longitudinal propagation to redistribute the incident field. Increasing a low-frequency component at fixed initial electromagnetic energy enhances the scalar response on one background and suppresses it on another. A calculation that propagates the field and its momentum, then their quadratic scalar and
geometric sources, predicts this reversal before nonlinear
evolution. At the first suppression comparison, the coherent profile error is $0.38\%$, against $46.9\%$ when cross terms are omitted. The selected response develops into a
magnetic pulse with electric and scalar exchange. The critical geometry thus preserves incident coherence as information that predicts its first departure from a Kasner epoch.
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General Relativity and Quantum Cosmology · Cross-listed from hep-th
Diffeomorphism-invariant Approach to Asymptotically Safe Quantum Gravity
Friederike Ihssen, Benjamin Knorr, Silas Mezger et al. (+2 more)
We provide a novel diffeomorphism-invariant approach to asymptotically safe metric
quantum gravity. It is based on physics-informed renormalisation group flows with a renormalisation group kernel that guarantees diffeomorphism invariance at each renormalisation group step. Importantly, it also allows us to control and maintain the relevance counting of operators in metric
quantum gravity. The resulting effective action is
quantum diffeomorphism-invariant and background-independent. As a first non-trivial application, we compute the Reuter fixed point in a manifestly diffeomorphism-invariant way. This computation is augmented with a detailed discussion of regularisation dependence and a systematic estimate of the errors arising from approximations.
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All authors Friederike Ihssen, Benjamin Knorr, Silas Mezger, Jan M. Pawlowski, Paul P. Sprenger
General Relativity and Quantum Cosmology · Cross-listed from hep-th
Unitary quantum conformal Bondi-Metzner-Sachs field theories
Daniel Grumiller and Iva Lovrekovic
We impose unitarity constraints on two-dimensional field theories whose
symmetries form the
quantum conformal Bondi-Metzner-Sachs
algebra, which combines conformal
symmetries with asymptotic
symmetries of asymptotically flat spacetimes. Positivity constraints put bounds on the central charge, 0<c<2.053. Positivity of the associated vertex
algebra allows only four central charges, c = 1, 3/2, 13/7, 2. Thus, only four candidates for
unitary field theories remain. We calculate their spectra of primaries and show that they are compatible with BPS-like and holographic inequalities.
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General Relativity and Quantum Cosmology · Cross-listed from hep-th
SolutionsX: supergravity theories/solutions as code, with an agentic workflow for machine-verifiable physics
Vasil Dimitrov
A supergravity solution in the literature is an artifact that cannot be verified without re-deriving it: conventions might not be clearly stated, papers have typos,
algebra is tedious. SolutionsX is a Mathematica package that turns an xAct environment, whatever physics it may describe, into a stored, machine-verifiable record: code that replays in a fresh kernel, carries its own verification, and can later be fetched for re-use or extension. The shipped examples are supergravity theories and their solutions, but the scope is anything xAct reaches: abstract tensors, differential forms, spinors in any dimension. We follow one published solution through the entire workflow,
benchmark the package's component engine against xAct's, and report on three blind runs of an agentic workflow in which an AI coding
agent, given the package and a small toolkit, correctly codified a recent paper in under three hours. A database of such records is useful to researchers today and gives
agents worked examples to learn from. The package acts as an internal verifier during the thought process of an
agent: a claim is checked in the kernel before it is made.
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General Relativity and Quantum Cosmology · Cross-listed from hep-th
Logarithmic correction to the entropy of near-extremal higher-curvature black holes
Pablo Bueno, Pablo A. Cano, Robie A. Hennigar et al. (+3 more)
The spherically symmetric sector of broad classes of $D$-dimensional gravitational theories can be effectively described by general two-dimensional Horndeski theories. Exploiting this correspondence, we study the low-temperature dynamics of near-extremal black hole solutions of the parent theories by deriving a universal near-horizon effective description in terms of Jackiw–Teitelboim (JT)
gravity. We explicitly show that the logarithmic
quantum correction to the
entropy, $S_{\rm JT}=\frac{3}{2}\log \left(T/T_{\rm breakdown} \right)$, previously derived for near-extremal black holes in Einstein
gravity coupled to matter from the one-loop exact JT partition function, is universal across all models admitting an effective two-dimensional Horndeski description. We determine the general form of the scale at which this correction becomes dominant, $T_{\rm breakdown}$, in terms of the data of the $D$-dimensional theories. We illustrate our general results with charged black holes in Lovelock gravities and regular black holes in Quasitopological gravities.
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All authors Pablo Bueno, Pablo A. Cano, Robie A. Hennigar, Javier Moreno, Ángel J. Murcia, Guido van der Velde
General Relativity and Quantum Cosmology · Cross-listed from astro-ph.IM
Search for Long-Transient Gravitational Waves from Supernova SN2023ixf using GFH-v2 Pipeline
Sandhya Sajith Menon, Lorenzo Pierini, Pia Astone et al. (+24 more)
We present a directed search for long-transient gravitational waves from the possible newborn magnetar remnant of SN2023ixf, a nearby Type II core-collapse
supernova in the M101
galaxy. The analysis uses LIGO Hanford and Livingston data from Engineering Run 15, using coincident data lying within the on-source window associated with the
supernova. We target signals from a rapidly rotating, non-axisymmetric
neutron star whose
spin-down is dominated by gravitational-wave emission, producing a power-law decrease in frequency and a corresponding decrease in strain amplitude. The search is performed with the GFH-v2 pipeline, based on the Generalized Frequency Hough transform. No candidate survives the coincidence and follow-up analysis. We therefore set upper limits on the maximum detectable distance as a function of initial frequency and ellipticity. For the highest ellipticity interval, the 90% upper limits reach distances of about 1-2.5~Mpc across most of the analysed band. Although these limits are below the distance to M101, the search provides the first application of GFH-v2 to a nearby core-collapse
supernova and characterizes its performance on real detector data.
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All authors Sandhya Sajith Menon, Lorenzo Pierini, Pia Astone, Cristiano Palomba, Francesco Safai Tehrani, Lorenzo Silvestri, Ornella Juliana Piccinni, Simone Dall'Osso, Stefano Dal Pra, Sabrina D'Antonio, Sergio Frasca, Dafne Guetta, Paola Leaci, Michal Bejger, Alicia Calafat, Evan Goetz, Rafel Jaume Amengual, Ian Jones, David Keitel, Andrzej Krolak, Iuri La Rosa, Andrew Melatos, Joan-Rene Merou, Lorenzo Mirasola, Claudio Salvadore, Alicia M. Sintes, Karl Wette
General Relativity and Quantum Cosmology · Cross-listed from astro-ph.HE
Bridging the Population Synthesis of Supermassive Binary Black Holes and the Gravitational Wave Background
Kanyuni Iemoto, Boris Goncharov, Gabriela Sato-Polito et al. (+1 more)
Pulsar Timing Arrays (PTAs) constrain population properties of supermassive binary black holes (SMBHBs) through the observation of the gravitational wave background (GWB). Unlike other approaches that interpolate population-synthesis libraries or only consider the mean of the strain spectrum, here we capture its full strain probability density directly from semi-analytic population models. We apply our new method to the semi-analytic SMBHB population model, independently reproducing the parameter estimation for this model performed by the NANOGrav Collaboration with their 15-yr data. We also show the extent to which discrete SMBHB contributions to the GWB resolve degeneracies in the population parameter space. Finally, using the source-count intensity as the intermediate product in our calculation, we map PTA observations, as a proof of principle, to the SMBHB model based on the
galaxy merger prescriptions from numerical hydrodynamical simulations "Illustris". We find the effect of delay times $\tau$ between kiloparsec and subparsec SMBHB separations following
galaxy mergers, finding $h_{\rm c}$ spanning $(1$-$6)\times10^{-16}$ and $N_{\rm c}$ spanning $(0.3$-$7.1)\times10^{-3}$ for $\tau$ up to 8 Gyr.
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All authors Kanyuni Iemoto, Boris Goncharov, Gabriela Sato-Polito, Xiaoming Bi
General Relativity and Quantum Cosmology · Cross-listed from astro-ph.GA
Improving constraints on the Yukawa correction at the Galactic Center with multiple stellar orbits
GRAVITY+ Collaboration: A. Foschi, K. Abd El Dayem, N. Aimar et al. (+76 more)
We investigate the presence of a Yukawa-like correction ($\propto \, \alpha e^{- r/\lambda}$) to Newtonian
gravity at the Galactic Center, using a multi-
star fitting code, including the newly discovered
star S$301$, to improve the constraints obtained using S$2$ orbit alone. We perform a Markov Chain Monte Carlo analysis using the astrometric and spectroscopic data of
stars S$2$, S$55$, S$29$, S$38$ and S$301$ collected by
GRAVITY,
GRAVITY$^+$, NACO and SINFONI instruments, covering the period from $1992$ to $2025$. Compared to
GRAVITY Collaboration 2025 (Paper I), in which only S$2$ was fitted, the tightest bound on the Yukawa coupling is again reached at $\lambda = 3\cdot10^{13}\,\rm m\ (\sim 200\,AU)$, where we find $|\alpha| < 6 \cdot10^{-4}$, an improvement of roughly a factor five. The addition of S$301$ extends the constraint to short ranges that were inaccessible to S$2$, yielding $|\alpha| < 0.004$ at $\lambda =10^{12}\,\rm m$ and $|\alpha| < 0.006$ at $\lambda =5\cdot 10^{11}\,\rm m$, while S$29$, with its larger apoapsis, gives $|\alpha| < 0.1$ at $\lambda \sim 2\cdot10^{15}\,\rm m$. The latter two represent the tightest limits at these scale lengths on a Yukawa correction obtained to date around a supermassive black hole.
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All authors GRAVITY+ Collaboration: A. Foschi, K. Abd El Dayem, N. Aimar, A. Berdeu, J.-P. Berger, G. Bourdarot, W. Brandner, Y. Cao, C. Correia, S. Cueves Cardona, R. Davies, D. Defrère, F. Delplancke-Ströbele, A. Drescher, F. Eisenhauer, L. Esteras Otal, M. Fabricius, H. Feuchtgruber, S. Flesch, N.M. Förster Schreiber, Q. Fournier, P. Garcia, R. Garcia Lopez, R. Genzel, S. Gillessen, F. Gonté, X. Haubois, S.F. Hönig, M. Houllé, S. Joharle, J. Kammerer, A. Kaufer, P. Kervella, L. Kreidberg, L. Labadie, S. Lacour, O. Lai, R. Laugier, J.-B. Le Bouquin, J. Leftley, R. Li, B. Lopez, D. Lutz, F. Mang, A. Mérand, F. Millour, M. Montargès, N. Morujão, H. Nowacki, M. Nowak, J. Osorno, T. Ott, S. Pappert, C. Paladini, T. Paumard, K. Perraut, G. Perrin, R. Petrov, N. Pourré, S. Rabien, D.C. Ribeiro, S. Robbe-Dubois, M. Sadun Bordoni, J. Sanchez-Bermudez, J. Sauter, J. Scigliuto, J. Shangguan, T.T. Shimizu, F. Soulez, C. Straubmeier, E. Sturm, M. Subroweit, C. Sykes, L.J. Tacconi, P. Thévenet, I. Urso, F.H. Vincent, J. Woillez, G. Zins
General Relativity and Quantum Cosmology
The generalized second law for Kerr-Taub-NUT black holes perturbed by test field
Koray Düztaş and Ahmet Cem Erdoğan
We evaluate the variations in the area and the
entropy of Kerr-Taub-NUT black holes perturbed by bosonic and fermionic test fields. We demonstrate that the critical frequency for a test field at which the variation of the area vanishes is strictly larger than the superradiance limit for Kerr-Taub-NUT black holes. Therefore both bosonic fields in the relevant range and fermionic fields which do not exhibit superradiant scattering can induce a decrease in the area of a Kerr-Taub-NUT black hole. However, the
entropy is not directly proportional to the area for Kerr-Taub-NUT black holes. Only fermionic fields with frequencies below the superradiance limit can induce an
entropy decrease. The simultaneous loss of
entropy by the black hole and the environment identifies a generic violation of the Generalized Second Law (GSL) for fermionic perturbations that fail to satisfy the Null Energy Condition (NEC). For bosonic perturbations that satisfy the NEC, we evaluate the limiting case, where a nearly extremal black hole is perturbed by a scalar field with frequency slightly above the superradiance limit. Our analysis reveals that the minimum increase in the black hole
entropy compensates for the
entropy loss of the environment, when one assigns Von Neumann
entropy to the test field. The GSL remains valid for perturbations satisfying the NEC.
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General Relativity and Quantum Cosmology
Global structure and stability of Kerr-Bertotti-Robinson spacetime
Yu-Sen Zhou, Liang-Bi Wu, Ming-Fei Ji et al. (+3 more)
The surface $r=\infty$ of the Kerr-Bertotti-Robinson spacetime is not a genuine boundary. We construct its natural analytic extension and show that $r=+\infty$ of one KBR region is smoothly connected to $r=-\infty$ of a neighboring one. Repeated continuation produces an infinite chain of regions connected by wormhole-like bridges and exposes the neighboring ring singularity without an intervening horizon, which violates the weak
cosmic censorship
conjecture. We then study a test massless scalar field on a two-universe scattering segment to probe the stability of the spacetime. For axisymmetric perturbations, we analytically establish purely imaginary growing quasinormal modes for every $\ell$ and trace their origin to the chronology-violating region. In the $(\ell,m)=(2,2)$ sector, unstable branches occur for sufficiently large rotation and sufficiently small
magnetic field. Their marginal real modes obey an exact horizon-flux balance, supporting a black-hole-bomb interpretation in which superradiant extraction is amplified by trapping within the double-barrier potential. The same cavity also supports families of weakly damped modes and may produce echo-like responses.
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All authors Yu-Sen Zhou, Liang-Bi Wu, Ming-Fei Ji, Wen-Tao Fu, Li-Ming Cao, Rong-Gen Cai
General Relativity and Quantum Cosmology
Matter-induced global regularity in non-polynomial quasi-topological gravity with Born-Infeld electrodynamics
Hong-Lin Liu, Zhong-Wen Feng, Qing-Quan Jiang et al. (+2 more)
We construct exact static, spherically symmetric charged solutions in four-dimensional non-
polynomial quasi-topological
gravity coupled to Born-Infeld electrodynamics. We focus on the model $h(p)=p/(1+\ell^{2}p)$, whose
vacuum branch develops a
curvature singularity at a finite radius. We show that Born-Infeld nonlinearities can remove this singularity within a finite region of parameter space, yielding globally regular geometries with an asymptotically flat exterior and a finite-
curvature AdS-type core. The regular sector contains both horizonless configurations and RBHs, separated by a degenerate-horizon boundary. We further identify a continuous branch of regular black holes with a triple-degenerate inner horizon and a simple outer event horizon, satisfying $\kappa_-=0$ and $\kappa_+\neq0$. These results provide a converse example to cases in which introducing charge spoils the regularity of a black hole that is regular in
vacuum. In the present model, Born-Infeld electrodynamics instead removes the finite-radius singularity of a gravitational branch that is singular in
vacuum and supports globally regular charged geometries, including regular black holes with nontrivial inner-horizon structure.
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All authors Hong-Lin Liu, Zhong-Wen Feng, Qing-Quan Jiang, Xia Zhou, Xue-Ling Mu
General Relativity and Quantum Cosmology · Cross-listed from hep-th
Can one hear the shape of a black hole singularity?
Sean A. Hartnoll and Alexander Zhiboedov
We compute the large overtone quasinormal frequencies $\omega_n$ of asymptotically AdS black holes with interior near-singularity Kasner epochs. We show that the Kasner exponents can be extracted cleanly from the large $n$ behaviour of the dispersion $\partial \omega_n/\partial k^2$ at $k=0$, where $k$ is a boundary momentum. We show that Kasner transitions, as occur in BKL near-singularity chaos, are audible in the quasinormal frequencies and reveal a map between overtone number $n$ and proper time to the singularity. Our results are obtained using a WKB analysis that isolates non-analytic exponents, determined by the near-singularity spacetime, from non-universal data such as the optical distance from the boundary to the singularity. We check our formulae in several numerical models.
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General Relativity and Quantum Cosmology · Cross-listed from quant-ph
Stationary states for a particle in a box with slanted walls
Nivaldo A. Lemos
The
quantum mechanical problem of a particle in a infinite potential well with slanted walls is studied. The energy
eigenvalues are determined by a transcendental equation involving the Airy function of the first kind. Two limiting cases are discussed. Next, the allowed energies are found by graphical and numerical methods. The graphical analysis hints that for large
quantum numbers the consecutive energy levels get arbitrarily close together. This asymptotic behavior of the energy spectrum actually holds, as shown by means of an intuitive argument and confirmed by resorting to basic properties of Airy functions. In a sense, Bohr's correspondence principle is more accurately fulfilled than in the cases of the standard particle in a box or the harmonic oscillator. A state is regarded the more confined the less the probability of finding the particle in the classically forbidden region. For some stationary states the confinement degree is calculated and a comparison is made with the harmonic oscillator, for which the ground state is the least confined of all stationary states. In the symmetric case — right and left walls of equal slope — something unexpected happens: beyond a certain critical slope the ground state is no longer the least confined eigenstate. Over and above its interesting physical features, this problem provides students with the opportunity to get acquainted with Airy functions, which do not belong to the standard mathematical repertoire of physics undergraduates.
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General Relativity and Quantum Cosmology
Thermodynamics and phase transitions of spherically symmetric AdS regular black holes
Qi-Quan Li, Yu Zhang and Hoernisa Iminniyaz
We obtain the singular ”mother” black hole solution by solving the coupling between Einstein
gravity with a cosmological constant and a nonlinear electromagnetic field. The thermodynamic quantities of the ”mother” black hole are first derived in the unconstrained phase space $(S, q, \alpha, P)$, after which the regularity condition $M = q^3/\alpha$ is imposed to obtain the thermodynamic quantities of a class of spherically symmetric AdS regular black holes self-consistently. We distinguish two categories of thermodynamic quantities: fundamental conjugate variables defined by the first law, and thermodynamic response functions constructed from them. For response functions involving second-order derivatives – in particular the heat capacity – we show that the order of constraint imposition and derivative calculation cannot be interchanged, and the correct procedure is to first impose the constraint and then construct the response function. Within this framework, we find that when $P<P_c$, the $G$–$T$ diagram exhibits a behavior qualitatively different from the swallowtail behavior of the standard RN-AdS black hole. Instead, it exhibits an 8-shaped structure for $P<P_z$ and a C-shaped structure for $P_z<P<P_c$, corresponding to first-order and zeroth-order phase transitions between small and large black hole phases, respectively. Imposing the regularity condition thus leads to a richer phase structure for this class of black holes than the standard RN-AdS case.
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General Relativity and Quantum Cosmology
Binary Black Holes in Einstein-Maxwell-Dilaton Theory: Second Post-Newtonian Dynamics from Effective Field Theory
Pawan Kumar Gupta
The detection of gravitational waves from compact binary coalescences provides a powerful opportunity to test general relativity in the strong-field regime and to search for signatures of alternative theories of
gravity. In this work, we consider Einstein-Maxwell-Dilaton (EMd) theory, in which black holes can carry both electric and scalar (dilatonic) charges. We employ the effective field theory approach, together with a temporal Kaluza-Klein decomposition of the metric in terms of non-relativistic gravitational fields, to derive the conservative two-body Lagrangian for charged black-hole binaries in EMd theory through second post-Newtonian (PN) order. Our calculation extends the previously known conservative dynamics at 1PN order and includes the gravitational, electromagnetic, and dilaton interactions at 2PN order. We verify the result in the appropriate Einstein-Maxwell, scalar-tensor, and general relativistic limits, and perform an independent test-body-limit check of the static 2PN sector. These results provide the conservative dynamics needed for developing higher-accuracy waveform models and testing EMd theory with gravitational-wave observations.
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General Relativity and Quantum Cosmology · Cross-listed from astro-ph.HE
Timing Gravity with Pulsars in the Strong Field
Riccardo Della Monica and Ivan de Martino
We propose a novel approach for the timing of
pulsars orbiting a supermassive black hole, which implements the fully relativistic calculations of the
photon travel time into a robust timing model. We generate realistic mock catalogues of
pulsar times-of-arrival for several putative
pulsars on tight orbits around the Galactic Center supermassive black hole, Sagittarius A* (Sgr A*). Then, we perform a proof-of-concept sensitivity analysis to forecast the accuracy that future observational facilities, like the Squared Kilometer Array, will achieve in the characterization of the parameters of our timing model. Our analysis shows how the observation of
pulsars at the Galactic Center will open an incredibly promising avenue for the characterization of the physical properties of Sgr A*, which can improve by at least three orders of magnitude the current constraints on the black hole's mass achieved with the S-
stars and event-horizon scale observations.
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General Relativity and Quantum Cosmology
Black Holes Thermodynamic Topology in Sharma-Mittal Statistics
Issam Najma, Yahya Ladghami, Amine Bouali et al. (+1 more)
In this study, we explore the thermodynamic
topology of black holes within the Sharma-Mittal
entropy framework. Our study covers several black hole solutions, including charged and uncharged black holes in $d$-dimensional, as well as Schwarzschild and Reissner-Nordström black holes. By introducing the Sharma-Mittal
entropy characterized by two parameters $\delta$ and $R$, we explore how deviations from the standard Boltzmann-Gibbs statistics modify the thermodynamic structure and stability properties of these systems. Using Duan's $\Phi$-mapping theory, we compute the corresponding topological numbers and classify black holes into distinct topological categories according to the winding number $W$. Moreover, our analysis shows that, within the Sharma-Mittal formalism, the topological classification is independent of spacetime dimension in the case $d>4$, although dimensions higher than four exhibit distinct features compared to the four-dimensional Schwarzschild and Reissner-Nordström black holes, reveal different behavior of thermodynamic
topology under generalized statistics.
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All authors Issam Najma, Yahya Ladghami, Amine Bouali, Taoufik Ouali
General Relativity and Quantum Cosmology · Cross-listed from astro-ph.CO
Conformally Interacting Dark Energy with Early and Late-Time Measurements
Shambel Sahlu, Abunie Gezahegn, Amare Abebe et al. (+2 more)
The conformal interacting dark energy (CIDE) model is investigated by introducing a scalar field representing dark energy (DE) coupled to dark matter (DM) via a conformal transformation, thereby yielding a class of scalar-tensor theories. The interaction term ${Q}$, that indicts the flow of energy between the dark sectors is proportional to the trace of the energy momentum tensor of the DM fluid, $T^{\mathrm{DM}}_{\mu\nu}$, as ${Q}=\frac{C'(\phi)}{2C(\phi)}g^{\mu\nu}T^{\mathrm{DM}}_{\mu\nu}$, where $C(\phi)$ is the conformal function of a scalar potential (coupling) field. We assume the power-law parametrization $C(\phi)\propto (1+\phi)^m$, with $m$ a coupling parameter, and determine the direction and magnitude of the energy flow between the DM and DE components. The dynamical nature of DE is modeled by the two conformal interacting scenarios, CIDE and $w$CIDE, with $w$ the DE equation of state parameter. To test the viability of each model, we constrain them using a combination of early- and late-time cosmological data, namely: CMB measurements from the South Pole
Telescope, Planck 2018, and the Atacama Cosmology
Telescope (DR6) (CMB SPA); BAO data from the Dark Energy Survey (DESI DR2 BAO); and
Supernova Type Ia distance compilations (PantheonPlus, PantheonPlus + SH0ES, Union3, and DES Dovekie). Parameter inference is performed with Monte Carlo Markov Chain (MCMC) simulations using COBAYA and a modified CLASS. Further statistical analysis using the Akaike information criterion (AIC) and the
Bayesian information criterion (BIC) is summarized to assess the viability of the model in comparison with the standard cosmological model, investigating the model's potential to alleviate the $H_0$ and $S_8$ tensions.
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All authors Shambel Sahlu, Abunie Gezahegn, Amare Abebe, Gonzalo J. Olmo, Diego Rubiera-Garcia
General Relativity and Quantum Cosmology
Exact Cancellation of Horizon Modes in Kerr Ringdown
Kei-ichiro Kubota, Yusuke Manita, Hayato Motohashi et al. (+1 more)
Ringdown gravitational waves probe black hole spacetimes via quasinormal modes (QNMs). Recent studies have reported oscillatory features in QNM-filtered waveforms, and have led to conflicting interpretations as to whether they represent a near-horizon "direct wave". Reexamining a particle plunging into a Kerr black hole, we show that the saddle-point approximation underlying the proposed interpretation fails near the horizon. Our exact analysis reveals that every source-induced horizon-mode pole is canceled by an infinite tower of Matsubara zeros, independently of orbital and black-hole parameters. The first four stages of this sequential screening are also confirmed by time-domain numerical integration. Thus, within the near-horizon perturbative framework, source-induced horizon-mode signals do not survive at late times.
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All authors Kei-ichiro Kubota, Yusuke Manita, Hayato Motohashi, Daiki Watarai
General Relativity and Quantum Cosmology
Darboux Isospectrality Constraints on Quasinormal Modes Deformed by Bumps
Zhen-Xiao Zhang, Chen Lan and Yan-Gang Miao
A localized Gaussian or Pöschl-Teller bump is widely used to probe the sensitivity of Schwarzschild quasinormal modes, where it is typically added to both the Regge-Wheeler and Zerilli potentials. We show that such an additive prescription is generically incompatible with the Darboux transformation connecting the two parity sectors. The reason is that such a transformation restricts a parity-blind bump to a fixed family of bumps with an unavoidable $r^{-2}$ tail, excluding any Gaussian or Pöschl-Teller profile with arbitrary amplitude, center, or width in the additive prescription. We give the complete classification of Darboux-admissible axial and polar pairs of bumps and propose two consistent scenarios: Darboux generator prescription in which a Gaussian or Pöschl-Teller profile is retained as a generator of the bump pair rather than as the bump itself, and Riccati completion prescription in which a Gaussian or Pöschl-Teller profile is regarded as one of the bump pair and its partner will be solved from the Riccati equation. Our frequency-domain calculations confirm that a finite and spurious axial-polar splitting of quasinormal modes will be produced if the Darboux-consistent scenarios are absent, while the centroid shift of the fundamental mode is nearly unchanged.
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General Relativity and Quantum Cosmology
Thin accretion-disc transfer functions in the q-metric spacetime: quadrupolar lensing signatures
Saken Toktarbay, Manas Khassanov, Aray Muratkhan et al. (+3 more)
We study geometrically thin equatorial disc images in the static, axisymmetric q-metric spacetime using backward ray tracing. The Schwarzschild solution is recovered at $q=0$; for the nonzero deformations considered here, $r=2M$ is a
curvature singularity rather than an event horizon. For a distant nearly face-on observer, we construct the first three equatorial transfer functions $r_m(b;q)$. In the {Schwarzschild} limit, the resolved third-crossing interval contains the critical impact parameter $b=3\sqrt{3}M$. As $q$ increases from $-0.3$ to $0.3$, the branch center shifts from $b_{3,c}/M\simeq3.716$ to $6.702$. In units of the physical monopole mass $\mathcal M=(1+q)M$, it instead decreases from $b_{3,c}/\mathcal M\simeq5.309$ to $5.156$. Much of the displacement in metric-parameter units therefore reflects the changing monopole scale. At fixed $\mathcal M$, the inclined first-intersection maps show that the contour dimensions increase with $q$, with larger relative changes near the inner disc. A prescribed power-law emissivity and relativistic frequency-shift weighting yield direct images whose integrated flux differs from the Schwarzschild value by at most $2.4\%$. Between the endpoint models, the horizontal median-flux position increases by $8.8\%$ and the interquartile width by $14.5\%$. Within this emission prescription, the residual deformation dependence appears mainly as a displacement and broadening of the brightness distribution. Higher-order radiative contributions are not included.
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All authors Saken Toktarbay, Manas Khassanov, Aray Muratkhan, Zhantay Muratkhan, Aliya Taukenova, Hernando Quevedo
General Relativity and Quantum Cosmology
The (in)stability on total transmission modes with small bumps
Xi-Ning Dong, Liang-Bi Wu, Yu-Sen Zhou et al. (+1 more)
Total transmission modes (TTMs) are a class of reflectionless solutions to black hole perturbation equations, closely related to quasinormal modes (QNMs), and can exhibit significant sensitivity to weak environmental perturbations. In this work, we investigate the spectrum (in)stability of TTMs of Tangherlini black holes by introducing a localized Pöschl-Teller bump perturbation into the effective potential, and employ a modified Chebyshev-Lobatto grid to improve the numerical accuracy of the localized perturbation. For $d=14$, $\ell=2$, and $s=2$, the purely imaginary TTM exhibits relatively strong spectrum stability, whereas the genuine complex TTMs undergo significant migrations even for small perturbations, consistent with the spectrum stability revealed by previous pseudospectrum analyses.
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All authors Xi-Ning Dong, Liang-Bi Wu, Yu-Sen Zhou, Zong-Kuan Guo
General Relativity and Quantum Cosmology
A New Window for Testing the PPN in the Strong-Field Regime: Stellar Rotation of S301
Mohsen Khodadi and Salvatore Capozziello
The recently discovered S301
star, with an orbital period of 8.7 years and eccentricity $e = 0.982$, reaches a pericenter of just $140\,R_{\mathrm{s}}$ — approximately nine times closer than S2's $\sim 1200R_{\mathrm{s}}$ — offering an unprecedented laboratory for testing strong-field
gravity. We demonstrate that S301's stellar
spin precession provides a novel probe of the PPN parameter $\gamma$, scaling as $(2\gamma_{\mathrm{PPN}} + 1)/3$ relative to general relativity (GR). For maximum projected velocity shifts of $46.1~\mathrm{km\,s^{-1}}$, next-generation spectrographs could constrain $\gamma_{\mathrm{PPN}}$ to $\sim 10\%$ precision. When combined with S301's orbital precession — a substantial $\sim 1.95^\circ$ pericenter advance per orbit (GR prediction), approximately an order of magnitude larger than S2's $\sim 0.2^\circ$, constraining $(2\beta_{\mathrm{PPN}} + 2\gamma_{\mathrm{PPN}} - 1)/3$ — the
spin measurement breaks the $\beta$-$\gamma$ degeneracy. A MCMC analysis of projected S2 and S301 observations yields $\sigma_\beta \approx 2.3 \times 10^{-4}$, with the $\gamma$ precision limited by the
spin precession measurement to $\sigma_\gamma \approx 0.1$. While the
spin precession provides an independent consistency check, its true significance lies in probing
gravity at $\phi/c^2 \sim 10^{-4}$ and $v/c \sim 0.08$ — four orders of magnitude stronger than Solar System tests and an order of magnitude stronger than current S-
star constraints. This complementary approach opens a new window for testing the PPN framework in the strong-field regime and demonstrates the power of combining multiple stellar probes at the Galactic Center.
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General Relativity and Quantum Cosmology
The Dynamical Instability of Rotating Boson Stars
Kai-Dong Zhou, Shou-Shan Bao, Jian Deng et al. (+1 more)
We investigate the dynamical instability of rotating
boson stars described by the Gross–Pitaevskii–Poisson equations with contact self-interactions. Through three-dimensional simulations, we confirm that the rotating
boson star undergoes a quasiperiodic conversion between ring-like and twin-
star-like density configurations in the early nonlinear stage. We develop a systematic linear stability analysis to identify the modes driving this instability and show that repulsive self-interactions could significantly increase the lifetime of the rotating
boson stars. We further construct a three-mode
Hamiltonian to describe the early nonlinear stage, which explains the quasiperiodic conversion. This analytical framework agrees reasonably well with the simulation results and provides a clear picture to understand the dynamics of rotating
boson stars.
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All authors Kai-Dong Zhou, Shou-Shan Bao, Jian Deng, Hong Zhang