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Physics General Relativity and Quantum Cosmology

gr-qc Watch General Relativity and Quantum Cosmology

Wednesday 19 August

General Relativity and Quantum Cosmology · Cross-listed from hep-ph

Bayesian Forecasts on Cosmic Superstring Searches with LISA

Satyabrata Datta and Rome Samanta

Cosmic superstrings are well-motivated early-Universe sources of stochastic gravitational waves, with phenomenology controlled by the string tension $G\mu$ and the intercommutation probability $P$. We study whether LISA can reconstruct these parameters and distinguish different superstring signal models in the presence of instrumental noise and astrophysical foregrounds. We consider two phenomenological models. In Model I, reduced intercommutation acts only as an amplitude enhancement of a cusp-dominated spectrum, $\Omega_{\rm SS}^{\rm I}=P^{-\beta}\Omega_{\rm cusp}$. In Model II, the signal is a cusp–kink mixture, $\Omega_{\rm SS}^{\rm II} =P^{-\beta}[p_c\Omega_{\rm cusp}+(1-p_c)\Omega_{\rm kink}]$, so that $P$ controls both amplitude and spectral shape. Using simulated LISA data, we perform Bayesian inference with noise uncertainties, unresolved extragalactic compact-binary backgrounds, and a flexible Galactic double-white-dwarf foreground. We compare the models using Bayesian evidences and map the $(G\mu,P)$ posterior geometry with marginalized widths, correlations, covariance anisotropy, principal eigenvalues, posterior area, and bias. We find that reduced intercommutation generically produces strong $G\mu$–$P$ correlations, because the data often constrain an amplitude-like combination. However, when the cusp–kink spectral difference lies in the LISA band and the signal is sufficiently loud, Model II can be favored and the posterior can retain genuine shape information. As an optimistic foreground scenario, we also compute the Bayes factor using a reduced tanh Galactic foreground template, finding improved model discrimination when the foreground shape is constrained.
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General Relativity and Quantum Cosmology · Cross-listed from astro-ph.HE

Modeling Relativistic Tidal Disruptions of MESA Stars

Liam M. Wang, Giovanni Maria Tomaselli and Zihan Zhou

Tidal disruption events (TDEs) occur when a star passes so close to a black hole that its self-gravity is overcome by the external tidal field. As the star passes, it initially deforms, then is ripped apart, and some of its material eventually falls back on bound orbits, forming an accretion disk around the black hole. A Newtonian model of TDEs, based on stellar perturbation theory of MESA stars, was recently introduced as an alternative to computationally intensive hydrodynamical simulations. In this work, we add relativistic corrections to the model, incorporating equatorial Kerr geodesics, relativistic tidal fields, and relativistic fallback times. Compared to the Newtonian case, we find that stars are disrupted earlier in their orbit, which gives them less time to accumulate physical deformations. Additionally, we find that the increased distance from the black hole at the time of disruption makes the fallback time longer. However, the black hole spin has a negligible impact on fallback time, except for orbits with exceptionally close pericenter. Our results allow for a more accurate calculation of fallback rates than the Newtonian model, while also remaining computationally cheap. The code is available on GitHub.
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General Relativity and Quantum Cosmology

Action-level characterization of gravitational-wave propagation in dynamical Barbero–Immirzi gravity

Zhi-Fu Gao, Hui Wang, Luiz Carlos Garcia de Andrade et al. (+3 more)

We investigate which operators in first-order dynamical Barbero–Immirzi (BI) gravity control cosmological tensor propagation at the action level. Within a bosonic, two-derivative, curvature-linear Einstein–Cartan class, eliminating the algebraic Lorentz connection reveals a separation between the scalar sector and the tensor kinetic normalization. In particular, the Holst-to-Palatini ratio determines the scalar kinetic structure, whereas the transverse-traceless tensor mode is normalized by the parity-even Hilbert–Palatini coefficient. As a consequence, a minimal dynamical Holst sector with fixed parity-even normalization remains exactly on the general-relativistic tensor-propagation surface and does not generate anomalous gravitational-wave friction. We then construct a regular nonminimal parity-even realization in which the tensor normalization evolves cosmologically, derive the corresponding standard-siren observable, and apply current GWTC-3, GWTC-4.0, and GWTC-5.0 information as an observational test of this action-level tensor sector. The resulting constraints should therefore be interpreted as limits on the evolution of the tensor kinetic normalization rather than direct constraints on minimal BI torsion dynamics.
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All authors Zhi-Fu Gao, Hui Wang, Luiz Carlos Garcia de Andrade, Na Wang, Guo-Qiang Jin, Zhou-Jian Cao

General Relativity and Quantum Cosmology · Cross-listed from hep-th

Stochastic Schwinger Effect: de Sitter and beyond

Lucas Vicente García-Consuegra and Azadeh Maleknejad

We develop a stochastic formulation of the Schwinger effect in de Sitter spacetime using the Schwinger–Keldysh (in-in) formalism, tailored to particle production by non-stationary gauge backgrounds in the early Universe. Treating the gauge field as a prescribed classical stochastic ensemble, we integrate out massless charged matter and derive the corresponding influence functional and particle-production kernel to leading non-trivial order in the gauge coupling. Conformal invariance allows the result to be extended directly from de Sitter to generic spatially flat FLRW spacetimes, without relying on asymptotic out states. We establish the infrared safety and classicality conditions of the stochastic description and clarify its relation to the conventional static Schwinger effect. We further extend the framework to massless conformally coupled scalars and to weakly coupled non-Abelian gauge sectors, including Standard Model and hidden-sector examples, in regimes where thermal corrections are negligible. Our results provide a general framework for matter creation by stochastic gauge fields in inflation, preheating, and non-thermal BSM sectors, connecting quantum field theory in curved spacetime with early-Universe and high-energy phenomenology.
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General Relativity and Quantum Cosmology · Cross-listed from hep-th

Krylov complexity and the growth of the black hole interior in 3D gravity

Arpan Bhattacharyya, Sounak Pal and Juan F. Pedraza

We investigate the growth of the black hole interior in three-dimensional gravity from the boundary theory. For the two-sided BTZ black hole, we propose a boundary reconstruction of the time dependence of a codimension-one surface in terms of correlation functions of smeared operators in the thermofield double state, reproducing the characteristic late-time linear growth predicted by the complexity-volume proposal. Using the Chern–Simons formulation of three-dimensional gravity, these nonlocal correlators are represented by bulk Wilson lines with smeared endpoints, extending the familiar connection between Wilson lines and codimension-two observables underlying holographic entanglement entropy to codimension-one observables. We then ask whether the same geometric growth is captured by Krylov complexity. For the smeared operators, we extract the Lanczos data from their correlation functions and find that operator Krylov complexity reproduces the late-time linear growth of the black hole interior, extending previous connections between operator growth and bulk geometry to AdS$_3$. By contrast, the Krylov spread complexity of the thermofield double state, obtained from the semiclassical gravitational partition function, does not exhibit the linear growth of the bulk volume within the regime accessible to our analysis. Our results therefore point to a distinguished role for operator Krylov complexity in encoding black hole interior growth beyond two-dimensional gravity, while highlighting a qualitative distinction between operator and state notions of Krylov complexity.
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General Relativity and Quantum Cosmology · Cross-listed from hep-th

Quantum effects of charged massive scalar fields on charged black hole space-times

Cormac Breen, George Montagnon, Peter Taylor et al. (+1 more)

We compute the renormalized expectation values of the scalar condensate, charge current and stress-energy tensor for a massive charged quantum scalar field on a Reissner-Nordstrom black hole. The mass of the scalar field is sufficiently large that classical superradiance is absent. We present results for the Boulware, Unruh and Hartle-Hawking states. Renormalized expectation values in the Hartle-Hawking state are computed using an efficient and accurate mode sum prescription, and for the other two states we employ state subtraction. The efficiency of our numerical method enables us to explore a large part of the parameter space, including near-extremal black hole charges and scalar field masses close to the superradiant limit.
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All authors Cormac Breen, George Montagnon, Peter Taylor, Elizabeth Winstanley

General Relativity and Quantum Cosmology

Breakdown of Hydrodynamic Universality in Neutron Star Oscillations

Gabriel S. Denicol, Amanda Guerrieri, João V. M. Muniz et al. (+2 more)

Hydrodynamic universality refers to the property that different formulations of relativistic dissipative hydrodynamics yield identical predictions in the asymptotic long-wavelength regime. We show that neutron-star oscillations need not reach this regime. Because the finite stellar radius limits the accessible wavelengths and causality imposes a lower bound on microscopic relaxation times, the separation between microscopic and macroscopic scales can become insufficient for hydrodynamic universality to emerge. Comparing linear oscillations in relativistic Navier–Stokes and Israel–Stewart theories, we find that realistic bulk viscosities can produce sizeable modifications of the oscillation spectrum, even at the longest wavelengths. These results identify neutron-star oscillations as a direct probe of microscopic nonequilibrium dynamics beyond the leading hydrodynamic description.
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All authors Gabriel S. Denicol, Amanda Guerrieri, João V. M. Muniz, Gabriel S. Rocha, Raissa F. P. Mendes

General Relativity and Quantum Cosmology · Cross-listed from quant-ph

Strongly coupled atom-cavity systems under boundary modulation: simulating gravitational-wave effects

Patryk Michalski, Jerzy Paczos, Navdeep Arya et al. (+1 more)

One of the proposed platforms in which both quantum and general relativistic effects can become observable is an atom interacting with the electromagnetic field in a gravitational-wave background. The periodic modulation of field modes induced by variations of the spacetime metric modifies the atomic emission spectrum. Notably, the temporal modulation of the mode-frequency induced by a plane gravitational wave can be simulated through modulated boundary conditions, such as moving cavity mirrors. We analyze the impact of this modulation on atom-field interactions in the strong atom-cavity coupling regime, where Rabi oscillations occur. We show analytically that the modulation is resonantly enhanced, leading to measurable imprints in the atomic transition probability. This establishes a realistic and experimentally accessible platform for probing analogue general relativistic effects in quantum optical systems.
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All authors Patryk Michalski, Jerzy Paczos, Navdeep Arya, Magdalena Zych

General Relativity and Quantum Cosmology · Cross-listed from hep-th

Inflationary Bispectra and IR Physics from Quantum Simulators

Matthias Thomas Nowinski and Ivo Sachs

Bose-Einstein condensates have been used successfully as quantum simulators for early-universe particle production. Here we extend this analogy to the interacting theory. To this end, we compute the leading interaction terms expected in a general experimental setup that determine the 3-point correlations. We apply them to cosmologically motivated expanding model universes, but also periodically oscillating ones. While expanding scale factors do not necessarily lead to easily observable signatures due to experimental constraints on the realizable scale factor, periodically driven ones produce resonant correlators that grow linearly over time and lend themselves well to experimental detection. One direct application of this analysis is the experimental study of late-time infrared divergencies often discussed in the context of massless scalars in de Sitter space.
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General Relativity and Quantum Cosmology · Cross-listed from hep-th

3D Einstein action from 6D Kodaira-Spencer gravity

Johanna Erdmenger, Jonathan Karl, Jani Kastikainen et al. (+1 more)

In view of embedding 3D gravity into topological string theory, we show that the dimensional reduction of 6D Kodaira-Spencer gravity on $\text{AdS}_3\times S^3$, i.e. the low-energy description of twisted holography, contains a subsector that coincides with the action of chiral 3D gravity on $\text{AdS}_3$. Furthermore, we show that the full 3D Einstein action is obtained as the reduction of two independent complex-conjugate copies of 6D Kodaira-Spencer gravity. We perform the dimensional reduction explicitly at the level of the classical actions, extending our previous work that related the equations of motion of the two theories. Our reduction procedure is based on a novel rewriting of the non-local 6D Kodaira-Spencer action as a local 6D holomorphic Chern-Simons action for the gauge group $\mathrm{SL}(2,\mathbb{C})$, valid within a subsector of complex structure deformations that we identify. Our results provide a necessary step toward embedding the Euclidean path integral of 3D gravity into topological string theory.
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All authors Johanna Erdmenger, Jonathan Karl, Jani Kastikainen, Henri Scheppach

General Relativity and Quantum Cosmology

Quasinormal Modes, Partial Transmission Probabilities, and Hod's Conjecture of Charged Black Holes in Perfect Fluid Dark Matter within Kalb-Ramond Gravity

Zongyuan Qin and Zheng-Wen Long

Within the Kalb-Ramond field-induced Lorentz-violating gravity, we investigate the perturbation dynamics and quasinormal mode (QNM) spectra of a charged black hole immersed in perfect fluid dark matter. The background spacetime is characterized by the Lorentz-violating parameter tau, the electric charge Q/M, and the dark matter parameter lambda/M. Owing to the non-zero vacuum expectation value of the KR field, the metric function approaches 1/(1-tau) at infinity instead of 1, rendering the spacetime non-asymptotically flat. Under the test-field approximation, the equations of motion for three types of perturbations (scalar, electromagnetic, and axial gravitational) are reduced to Schrodinger-type radial equations with single-peak effective potentials. The QNM frequencies are cross-validated using the sixth-order WKB method and the time-domain Prony method, while the partial transmission probabilities are computed within the WKB scattering framework. Parameter scans show that tau exerts the strongest influence on the QNM spectrum, followed by lambda/M, with Q/M having the weakest effect; the same ordering holds for the partial transmission probabilities. Under the same parameters, the QNM frequencies of the three perturbations follow the order scalar > electromagnetic > gravitational, whereas the transmission probabilities exhibit the reverse order, reflecting the different impact of the effective potential height on the oscillation frequency and on the transmission probability. The Hod conjecture |Im(omega)| <= pi T_H holds throughout the parameter range examined.
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General Relativity and Quantum Cosmology

On entropic cosmology, late time acceleration and the quantum bounce

Luis Rey Diaz-Barron, G. E. Pérez-Cuéllar and M. Sabido

In this work, we present a unified entropic description of the quantum bounce that is present in Loop Quantum Cosmology (LQG) and dark energy that drives the late time acceleration of the Universe. By considering a minimal area $A_0$ for the Universe and a modified entropy area constructed as the sum of $S_Q$, $S_{BH}$ and $S_{DE}$, we derive the Friedmann equations. We show that in the limit $A\sim A_0$, there is a critical density that generates the quantum bounce and depends on the minimal area. Moreover, in the limit $A\gg A_0$ (large Universe) the late time dynamics gives an accelerating scale factor. Therefore, we can argue an entropic origin for the quantum bounce and dark energy.
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General Relativity and Quantum Cosmology

Notes on 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 (KBR) spacetime is not the collection of the endpoints of infinitely extended light rays, and the Coulomb type component of gravitational field strength represented by $\Psi_2$ remains nonvanishing there, indicating that this surface is not a real boundary. We construct a natural extension across this surface, which connects the exterior of one KBR region to the interior of a neighboring one and, upon iteration, produces an infinite chain of regions connected by wormhole-like bridges. The extension also exposes the neighboring ring singularity without an intervening horizon, challenging the weak cosmic censorship conjecture and raising the question of whether the extended geometry is stable under perturbations. We therefore study the quasinormal modes (QNMs) of a test massless scalar field on a two-universe scattering segment. For axisymmetric perturbations, the existence of purely imaginary unstable QNMs is analytically proved for every $\ell$, with their origin tied to the chronology-violating region. In the $(\ell,m)=(2,2)$ sector, unstable QNM branches driven by a black-hole-bomb mechanism are found. Finally, the wormhole geometry produces a double-barrier cavity and families of weakly damped QNMs, suggesting 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

Duru-Kleinert Path Integral in Unimodular Quantum Cosmology

Xiao-Kan Guo

The Wheeler-DeWitt equation of a flat Friedmann-Lemaitre-Robertson-Walker universe filled with pressureless dust and a cosmological constant in the unimodular gravity is recently shown to be equivalent to the radial Schrödinger equation of a hydrogen atom. In this paper, we revisit this correspondence between the unimodular quantum cosmology and the hydrogen atom by using the Duru-Kleinert path integration technique. The Duru-Kleinert time reparametrization transforms the Euclidean path integral of the universe into that of a one-dimensional Coulomb system. Through a Mellin-Barnes integral representation, we extract the bound state poles of the Green's function, which give the quantized negative cosmological constant. We compute the quantum tunneling rate from “nothing” to a universe directly within the Coulomb model. Furthermore, for a positive cosmological constant, we compute the spectral density and the Krylov complexity for the unbounded state.
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General Relativity and Quantum Cosmology · Cross-listed from hep-th

Perturbative Hairy Black Branes in the $G_{2}$-Invariant Sector of Dyonic ISO(7) Gauged Supergravity

Sangheon Yun

We construct perturbative black-brane solutions carrying neutral scalar hair in the $G_{2}$-invariant truncation of four-dimensional dyonic $\mathcal{N}=8$ ISO(7) gauged supergravity, an exact consistent truncation of massive type~IIA supergravity on $S^{6}$. Expanding around the $G_{2}$-symmetric AdS$_{4}$-Schwarzschild black brane in powers of a dimensionless scalar-charge parameter $\eps$, we show that the perturbation hierarchy reduces, order by order, to a nested sequence of inhomogeneous Legendre equations (demonstrated through second order). The first-order scalar satisfies a Pöschl–Teller equation with exact parameter $\nu(\nu+1)=2/3$, giving $\nu=-\frac{1}{2}+\frac{\sqrt{33}}{6}$, and the first-order metric is fixed algebraically by the same function, $A^{(1)}=-\tfrac{\sqrt{7}}{2}\phi^{(1)}$, so the entire $\mathcal{O}(\eps)$ sector is one Legendre function. An identity $\nu+1=\Delta_{+}/3$, with $\Delta_{+}=(3+\sqrt{33})/2\approx 4.372$ the conformal dimension of the dual scalar operator, relates the Pöschl-Teller parameter to the AdS/CFT dictionary via the nonlinear Fefferman-Graham map $z \propto z_{\mathrm{FG}}^{3}$. The $\mathcal{O}(\eps^{2})$ back-reaction yields explicit corrections to the renormalized free energy and Bekenstein-Hawking entropy density at fixed temperature, consistent with the first law; equivalently, at fixed entropy or energy density it lowers the Hawking temperature by $\delta T/T=\mathcal{O}(\eps^{2})$. For the leading transport coefficients the shear viscosity saturates $\eta/s=1/(4\pi)$, while the Eling-Oz horizon formula gives a nonzero bulk viscosity $\zeta/\eta=\bigl(\tfrac{\Delta_{+}-3}{2}\bigr)^{2}\eps^{2}=\tfrac{3(7-\sqrt{33})}{8}\eps^{2}\approx0.471\,\eps^{2}$. With $c_{s}^{2}=\tfrac12-\mathcal O(\eps^{2})<\tfrac12$, this indicates a softening of the equation of state.
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General Relativity and Quantum Cosmology · Cross-listed from astro-ph.IM

Estimation of systematic error from bulk deformation of end test mass induced by photon calibrator for LIGO post-O5 gravitational wave projects

Daiki Tanabe, Aloysius Niko, Kun-Yao Chang et al. (+4 more)

We studied the bulk deformation of the end test masses (ETMs) of gravitational wave (GW) detectors caused by calibration devices named Photon Calibrator (Pcal). This bulk deformation is one of the source of calibration error since it induces non-linear displacement from the ideal pendulum motion of the ETM. Particularly, it is the dominant error source above 1500 Hz which is crucial to the studies of neutron star mergers. The displacement also depends on beam offsets of the main interferometer (IFO) beam and Pcal beams. We conceptually described frequency dependent effect of bulk deformation and evaluated it in several cases of the beam offset with finite-element analysis (FEA) software, for ETM models of Advanced LIGO (aLIGO), KAGRA, Advanced Virgo (AdVirgo), and LIGO A#.
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All authors Daiki Tanabe, Aloysius Niko, Kun-Yao Chang, Yuki Inoue, Dripta Bhattacharjee, Richard Savage, Henry Tsz-King Wong

General Relativity and Quantum Cosmology · Cross-listed from hep-th

Non-abelian uni-vector deformations in gauged supergravities and non-abelian Einstein-Maxwell theories

Kirill Gubarev and Konstantin Sovit

We construct non-abelian uni-vector deformations of solutions in non-abelian Einstein\–Maxwell theories and gauged supergravities, obtained as Scherk–Schwarz reductions of general relativity and double field theory, respectively. We provide examples of deformed backgrounds for both cases. We show that non-abelian deformations in Einstein–Maxwell theories can be presented as coordinate transformations in the parent theory, general relativity, extending the result of arXiv:2508.09637 for abelian uni-vector deformations.
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General Relativity and Quantum Cosmology

A Quantum-Gravity-Motivated GUP Effective Metric

M. H. Al Ghifari, M. F. Fauzi, A. Rohim et al. (+3 more)

Recent critiques have addressed certain aspects of the generalized uncertainty principle (GUP) effective metric (Ong 2023). This study presents a scale-dependent quadratic GUP effective metric, constructed through analyses of the gravity-induced phase shift (COW experiment) and the Einstein-Bohr photon box Gedanken experiment. In contrast to the procedure outlined in (Xiang et al. 2018), the momentum-dependent metric is improved by introducing an interpolating function $\Delta p (r)$, which employs the effective distance concept to accurately capture the distinct behavior of $\Delta p (r)$ in both short and long distance regimes. The resulting effective metric exhibits the same structure as that derived from the Renormalization Group (RG) theory. However, the RG parameter $\hat{\gamma}$ can now be related to the dimensionless GUP parameter $\beta_0$, thereby distinguishing this metric from the RG-based approach. The corresponding effective metric prediction demonstrates internal consistency of the model, and phenomenologically the predictions are in agreement with some quantum black hole models in some limits. The effective metric improved black hole thermodynamics and shadow predictions compared to the heuristic approach and other proposed GUP effective metrics. Furthermore, the relationship between GUP and $f(R)$ gravity (D'Agostino et al. 2026) may provide a possible future route toward a more fundamental description of GUP.
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All authors M. H. Al Ghifari, M. F. Fauzi, A. Rohim, H. S. Ramadhan, H. Alatas, A. Sulaksono

General Relativity and Quantum Cosmology

Effective curvature coupling of link-based causal set propagators in $1+1$ dimensions

Arsim Kastrati

We study how a recently introduced causal-set propagator defined in terms of links responds to curvature. On sprinklings embedded in a flat 1+1-dimensional Minkowski space, this propagator is known to reproduce the massless retarded continuum Greens function on large scales. In conformally flat embeddings with constant curvature $\mathcal R$, the causal order is unchanged, but the link relationship is sensitive to the physical volume of the spanned causal diamond. We show that this volume dependence generates a leading curvature correction to the propagator. On large distances, this correction is equivalent to a continuum scalar propagator with an effective curvature coupling of the form $\xi \mathcal R$ with the coupling constant $\xi_{\rm eff}=1/6$, equivalently corresponding to an effective mass-squared parameter $m_{\rm eff}^2=\xi_{\rm eff}\mathcal R$. This coupling is not inserted by hand but emerges from the link-based path sum itself, reflecting the microscopic structure of the causal set. Numerical simulations on sprinklings embedded in $\mathrm{AdS}_{1+1}$ and $\mathrm{dS}_{1+1}$ support the predicted curvature response and indicate that the effective coupling persists as the sprinkling density is increased.
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General Relativity and Quantum Cosmology · Cross-listed from hep-ex

Technical Proposal for the Atom Interferometer CERN Experiment (AICE) Facility

Gianluigi Arduini, Nadja Augst, Mark G. Bason et al. (+79 more)

We present the technical proposal for the Atom Interferometer CERN Experiment (AICE), a $\mathcal{O}(100)$ m vertical atom interferometer to be installed against the wall of the PX46 access shaft to the LHC. AICE is conceived as a versatile and flexible long-baseline atom-interferometry facility whose primary scientific goal is probing for bosonic ultralight dark matter (ULDM) in a mass range inaccessible to other experiments, with a secondary goal of pioneering the exploration of gravitational waves (GWs) with frequencies in the range ${\sim}$0.03-3 Hz as a pathfinder for future longer-baseline detectors. The initial configuration employs ultracold $^{87}$Sr atoms in a single-photon 698-nm interferometer with three shaft-based atom sources in a multi-source gradiometer geometry, supported by one surface reference source for laser stabilisation and diagnostics, to target scalar ULDM. Operation with $^{88}$Sr will give sensitivity to axion-like particles (ALPs), vector ULDM with $B-L$ couplings and violation of the principle of equivalence, while a $^{171}$Yb upgrade will improve the sensitivity to $B-L$ couplings and equivalence violations. Probing the Einstein equivalence principle (EP) and measuring $\alpha$ will proceed in parallel with the ULDM searches. A conceptual feasibility study and a detailed technical implementation study have established that PX46 is a uniquely mature and implementation-ready site, with no technical showstoppers. Completing site preparation works during LS3 would enable the subsequent installation and operation of AICE without impacting HL-LHC operations. The detector design builds on the VLBAI and MAGIS experiments and the AION-10 Technical Design Report, scaling the strontium gradiometer architecture to the $\sim$100 m baseline. AICE is endorsed by the TVLBAI Proto-Collaboration, comprising 57 institutions in 22 countries.
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All authors Gianluigi Arduini, Nadja Augst, Mark G. Bason, Charles Baynham, Andrea Bertoldi, Gianfranco Bertone, Diego Blas, Daniela Bortoletto, Sougato Bose, Roberto Ales Bozzi, Oliver Buchmueller, Tamara Alice Bud, Clare Burrage, Sergio Calatroni, John Carlton, Vassilis Charmandaris, Maria Luisa Chiofalo, Pierre Cladé, Jonathon Coleman, Fabio Corsanego, Albert De Roeck, Arnaud Devienne, Fabio Di Pumpo, John Ellis, Pierre Fayet, Chris Foot, Elina Fuchs, Naceur Gaaloul, Susan Gardner, Enno Giese, Eduardo Granados, Saïda Guellati-Khelifa, Michael Guinchard, Timo Hakulinen, Tiffany Harte, Richard Hobson, Michael Holynski, Angelo Infantino, Alex Kehagias, Eva Kilian-Rademacher, Wolfgang Korsch, Damien Lafarge, Samuel Lellouch, Lucas Lombriser, Elias Lopez Asamar, J. Luis Lopez-Gonzalez, Michele Maggiore, Charline Marcel, Anna Marchant, Christopher McCabe, Gaetano Mileti, Peter Millington, Jeremiah Mitchell, Noam Mouelle, Angel Navascues Cornago, François Pillon, Rosa Poggiani, Johann Rafelski, Ernst M. Rasel, Maike Reckermann, Albert Roura, Rui Samoes, Federico Sanchez Nieto, Jack Sander, Carlo Scarcia, Jesse Schelfhout, Wolfgang Schleich, Dennis Schlippert, Ulrich Schneider, Steven Schramm, Florian Schreck, Olga Sergijenko, Marcelle Soares-Santos, Guglielmo M. Tino, Jonathan N. Tinsley, Tristan Valenzuela, Daniel Valuch, Maurits van der Grinten, Klaasjan van Druten, Ville Vaskonen, Wolf von Klitzing, Michael Werner

General Relativity and Quantum Cosmology

On uniqueness of non-vacuum stationary axisymmetric type D spacetime

Hiroaki Nakajima, Ya Guo and Wenbin Lin

We study a family of the non-vacuum stationary axisymmetric type D metrics, where the two principal null directions are geodesic and shearfree. It is demonstrated that the conformal-to-Carter metric gives the most general form of this family, without any assumptions which are previously used by Ovcharenko and Podolský to arrive at this conclusion.
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General Relativity and Quantum Cosmology · Cross-listed from astro-ph.CO

Broadband Chiral Primordial Gravitational Waves from Constant-roll Inflation in Parity-violating Symmetric Teleparallel Gravity

Xu Zhang, Chang Liu and Chengjie Fu

We investigate primordial gravitational waves (GWs) generated during constant-roll inflation in a parity-violating extension of symmetric teleparallel gravity. The parity-violating interactions leave the background evolution and linear scalar perturbations unchanged, while inducing velocity birefringence in the tensor sector. Consequently, one of the two circular polarization states undergoes tachyonic amplification, producing a strongly blue and nearly fully chiral tensor spectrum from the cosmic microwave background (CMB) to interferometer scales. We identify viable constant-roll parameter regions consistent with current CMB constraints and determine the largest coupling strength compatible with both CMB B-mode measurements and the LIGO-Virgo-KAGRA (LVK) O1–O4a bound on the stochastic GW background. The predicted CMB B-mode spectra may be detectable by LiteBIRD, while the enhanced high-frequency signal could be accessible to the LISA–Taiji network and LVK O5 run. The model also predicts nonvanishing TB and EB correlations. These results highlight the potential of combining CMB and multi-band GW observations to test parity-violating gravity during inflation.
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General Relativity and Quantum Cosmology

First Law of Black Hole Interior Dynamics

Ze-Xuan Xiong and H. Lu

We obtain a local first law of dynamics within the interior geometries that are governed by cosmological solutions connecting the event horizon and the Kasner-like singularity. Evaluating the Iyer-Wald identity between the horizon and near-singularity geometries, we define a Kasner potential and transported response coefficients. We test the first law by both exact and numerical solutions. Our formalism provides a self-consistent approach to study the interior dynamics without having to appeal to the outside geometry and the asymptotic charges. It may provide a new approach to study the phase structures of the interior dynamics.
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General Relativity and Quantum Cosmology

Covariant Energy Momentum Tensor in General Relativity by Generalized Canonical Method

Masakatsu Kenmoku

Defining a complete and covariant energy-momentum tensor in general relativity is a longstanding issue of concern. A widely attempted approach is to define it as a pseudo-tensor in an asymptotic Lorentz system. In this paper, we present a complete covariant definition of the gravitational energy-momentum tensor in the generalized canonical form. The key is incorporate higher-order differential terms of the metric tensor into the gravitational action in order to derive the energy-momentum tensor consistently. This completely covariant form ensures that the gravitational energy is correctly obtained in any coordinate system, including polar coordinates and asymptotic Lorentz systems.
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General Relativity and Quantum Cosmology

Bounds on the Lyapunov Exponent of Circular Null Orbits in $n$-Dimensional Black-Hole Spacetimes

Anagha V., C. Fairoos and T. K. Safir

Unstable circular null orbits provide a geometric bridge between black-hole optics, photon rings, strong gravitational lensing, and the eikonal sector of quasinormal ringing. In four-dimensional Einstein gravity, the instability rate of such orbits, measured by the Lyapunov exponent $\lambda$, obeys model-independent upper bounds when the matter sector satisfies standard energy conditions. We extend this analysis to static, spherically symmetric, asymptotically flat black holes in arbitrary dimensional Einstein gravity, allowing for an anisotropic matter distribution. We show that, under the tangential null energy condition, the Lyapunov exponent admits a dimension-dependent upper bound in terms of the generalized surface gravity $\kappa (r)$ and the metric function $\mu(r)$, both evaluated at the photon sphere $r =r_\gamma$. For $n$- dimensional black hole spacetime, the bound is $\lambda\leq\sqrt{n-3}\, {\kappa_\gamma}/{\sqrt{\mu_\gamma}}$. Related bounds are derived in terms of the critical impact parameter (shadow radius), the orbital frequency, a local acceleration scale, and eikonal quasinormal-mode damping. All principal inequalities reduce to the known four-dimensional results for $n=4$. Also, the bounds involving the critical impact parameter and orbital frequency are saturated by the Schwarzschild-Tangherlini vacuum solution. The results provide a compact set of consistency conditions linking the dimensionality of spacetime to the instability of photon trapping in Einstein gravity.
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Tuesday 18 August

General Relativity and Quantum Cosmology · Cross-listed from cs.MS

DSLHyPE-a DSL kernel language for the Exascale Hyperbolic PDE Engine ExaHyPE

Timothy J.R. Stokes, Nick Brown, Thomas A. Flynn et al. (+2 more)

We introduce a bilingual domain-specific language (DSL) for modelling compute kernels within a generic solver for hyperbolic partial differential equations (PDEs). Users express PDE terms, i.e.~the underlying physics, in a familiar native language such as C or C++, while the numerical scheme is specified in a Python-embedded DSL, DSLHyPE. DSLHyPE's compiler lowers the Python description to MLIR and introduces a translation pass that integrates it with native code likewise mapped to MLIR. Our approach keeps the numerical representation and the physics implementation separate for as long as possible, while delegating optimization to the compiler through existing MLIR optimization passes. This separation of concerns benefits researchers developing numerical schemes on top of existing PDE implementations or with applications involving nonlinear systems whose PDE terms must solve PDEs themselves. We demonstrate the feasibility of the approach using a gravitational-wave solver and a matter-evolution solver on x86 processors and H200 GPUs.
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All authors Timothy J.R. Stokes, Nick Brown, Thomas A. Flynn, Maurice Jamieson, Tobias Weinzierl

General Relativity and Quantum Cosmology

Thermodynamics, topology and non-Abelian instability of the five-dimensional Einstein–Yang–Mills black hole with exponential entropy correction

Aram Bahroz Brzo, Peshwaz Abdulkareem Abdoul, Behnam Pourhassan et al. (+1 more)

The five-dimensional Einstein–Yang–Mills black hole obtained from the higher-dimensional Wu–Yang ansatz carries a logarithmic non-Abelian contribution to the metric function, making it an analytically tractable setting for studying how gauge charge reshapes horizon thermodynamics beyond four dimensions. We derive expressions for the mass–radius relation, the Hawking temperature, the entropy, the Yang–Mills potential and the first law, and record the curvature invariants, which show that the logarithm sharpens the central singularity rather than smoothing it. A non-perturbative exponential entropy correction is then added, and the corrected heat capacity and free energies are obtained analytically. The geometry is extremal at $r_h=|Q|$ and the heat capacity diverges at $r_h=\sqrt{3}\,|Q|$, a Davies-type point. The correction moves that point inward, $r_{\rm tr}/|Q|\simeq\sqrt{3}-9\lambda\alpha\eta\,e^{-3\sqrt{3}\lambda}$. Using the generalized off-shell free energy we find a conserved topological charge $W=0$ carried by a stable–unstable defect pair whose inner member alone responds to the correction. We then solve the spherically symmetric magnetic Yang–Mills perturbation sector, which probes the gauge field itself rather than a test scalar. Two independent numerical schemes agree to better than $1.2\times10^{-7}$ and give a purely imaginary unstable mode whose growth rate falls monotonically from $\Gamma_{0}r_h=0.414753$ at $Q/r_h\to0$ to $0.317520$ at $Q/r_h=0.99$, passing through the Davies scale without any feature. Because the effective potential decays as $-9/(4r_{*}^{2})$, with a coefficient above the critical value $1/4$, the sector supports an infinite geometric tower of unstable modes accumulating at $\Gamma\to0$ with the charge-independent ratio $\Gamma_{n+1}/\Gamma_{n}\to e^{-\pi/\sqrt{2}}\simeq0.108453$, which we confirm numerically.
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All authors Aram Bahroz Brzo, Peshwaz Abdulkareem Abdoul, Behnam Pourhassan, Izzet Skalli

General Relativity and Quantum Cosmology

Renormalization group improved black holes in non-commutative momentum-dependent spacetime geometry

Gema Ilham Baskara Darman, Ar Rohim and Anto Sulaksono

We investigate black holes (BHs) in momentum-dependent spacetime geometry and assess its quantum Reissner-Nordström (RN) consistency with the weak gravity conjecture (WGC). Quantum corrections are introduced through the non-commutative momentum space algebra as the quantization process, and spacetime renormalization approach as a map between momentum and spacetime spaces. For the Schwarzschild case, thermodynamic analysis indicates the existence of a hot (non-zero temperature) BH remnant when evaporation stops (the entropy becomes zero), obeying a complementary third law for black hole thermodynamics. We extend this framework to the RN solution and examine its extremal limit. For large BHs with $M \gg M_P$ ($M_P$ for Planck mass), the quantum-improved RN geometry exhibits a non-zero Hawking temperature in the extremal case, consistent with the WGC, which stipulates that extremal states should not be exactly stable or cold. The resulting momentum-dependent metric and thermodynamic properties are shown to reproduce the results derived from the Poincaré algebra (classical model) in the infrared (IR) regime.
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General Relativity and Quantum Cosmology

Relational Wigner-Smith Duration in Wheeler-DeWitt Scattering

Daulet Berkimbayev

A closed Friedmann-Lemaitre-Robertson-Walker Wheeler-DeWitt model is formulated as an exact reflection problem. The derivative of its reflection phase defines a relational crossing duration whose first two clock moments follow from a covariant scalar-clock observable. An analytic expression is obtained for this duration, its classical recollapse limit, and the leading quantum correction. A finite spectral packet also gives an operational, equal-prior minimum error probability for distinguishing the two orientations of recollapse with a geometric reading. The construction is extended to a bounded finite quantum detector. Its multichannel reflection matrix yields probe transitions, spectral-probe correlations, and a matrix duration. A direct weak-coupling calculation verifies the predicted transition and duration scalings. Scalar-clock conditioning and oriented geometric sections are shown to be local representations of the same positive-frequency Dirac sector. These results define duration and transition observables entirely through correlations and scattering records of a stationary constrained state, without introducing a background clock.
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General Relativity and Quantum Cosmology

On the Tidal and Frame-Drag Fields in General Relativity

Rahulkumar Solanki

It is known that in vacuum, two infinitesimally separated timelike observers under free fall notice a relative acceleration due to the tidal field (or the `electric' part of the Weyl tensor), and if they are carrying inertial guidance gyroscopes, they notice relative precession between these gyroscopes due to the frame-drag field (or the `magnetic' part of the Weyl tensor). The frame-drag field thus has no Newtonian analog. In this paper, for a family of timelike observers carrying inertial gyroscopes and forming a congruence, we define these fields as constraint equations in the presence of matter using (1+3) covariant splitting of spacetime. Unlike Newtonian gravity, the relative velocities of the observers around a closed contour formed by their spatial separations (and a temporal vector that closes this contour if the congruence is not hypersurface orthogonal) do not add up to zero due to the frame-drag field and momentum density of the fluid. Moreover, the relative orientations of the gyroscope spins around the same contour do not generally cancel out due to the tidal field, the fluid variables (anisotropic pressure and energy density), and the spatial cross-product of relative velocities associated with the separation vectors that form the contour. Additionally, it is shown that even in the absence of the frame-drag field, neighboring observers see relative precession between their gyroscopes when their relative velocity and acceleration are non-parallel due to differential Thomas precession.
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