We obtain a tensionless limit of the M-theory 5-brane action and discuss its properties. The consistency of this limit requires that the field strength $H_3$ of the 2-form gauge field on the M5 brane worldvolume is nonvanishing and nondegenerate, so that one can also regard it as a strong $H_3$-field limit. The induced $6D$ worldvolume metric of this theory is nondegenerate in contrast to conventional tensionless (null) $p$-branes. We find that the tensionless M5-brane action is invariant under a super-Weyl symmetry acting on the bulk supergeometry, while in the purely bosonic case the action is invariant under an 11D target-space conformal symmetry, a property which is characteristic for the tensionless bosonic branes. Upon imposing a static gauge, which fixes worldvolume diffeomorphisms, this 11D conformal symmetry becomes a deformed 6D worldvolume conformal symmetry whose action on the worldvolume coordinates involves field dependent terms. When the transversal fluctuations of the 5-brane in the bulk are zero, the model reduces to the conformal nonlinear chiral 2-form electrodynamics considered earlier by Gibbons and West [J. Math. Phys. (N.Y.) 42, 3188 (2001)] and by Townsend [Proc. R. Soc. A 476, 20190863 (2020)].

We develop a geometric theory of information processing in the horizon-brightened acceleration radiation (HBAR) channel, in which the radiative horizon-area change provides an entropy budget for the information carried by the radiation field. Building on the quantum-optical description of atom-field interactions near the horizon and the resulting HBAR thermodynamic correspondence, we derive area-cost laws in the near-steady, thermally saturated regime. The accessible classical information and the mutual information generated between the radiation field and its environment are bounded by the associated radiative horizon-area budget. Reliability is incorporated through Fano’s inequality, which translates a prescribed decoding error probability into an area requirement. We further derive Fisher-information speed limits that constrain the statistical evolution of the radiation field and place a lower bound on the duration required for correlation generation. Together, these results establish a bits-per-area principle linking black-hole thermodynamics, information geometry, and quantum information in the HBAR framework.

We construct here a generalization of Joshi-Malafarina-Narayan (JMN) naked singularity spacetimes that arise as equilibrium end states of gravitational collapse with nonvanishing tangential pressure. The generalization introduces density inhomogeneity through a radially dependent mass function $F(r)=(M_0+M_n{r}^n)r^3$, leading to a two-parameter family of solutions matched smoothly to an exterior Schwarzschild spacetime. The observational properties of the spacetime are then examined through shadow formation and emission from accreting matter. We find that in this more general case, as well, when the photon sphere lies in the exterior Schwarzschild region, the shadow is identical to that of a Schwarzschild black hole. Accretion spectra show enhanced high–frequency emission compared to Schwarzschild, while deviations from the original JMN model remain small due to strong constraints on the inhomogeneity parameter. These results indicate that the generalized model effectively serves as a small perturbation of the JMN spacetime, demonstrating the robustness of the physical properties of the original JMN-type naked singularity geometries.

We investigate the fluid interpretation of the proper kinetic gravity braiding contribution to the stress tensor of minimally coupled scalar fields for timelike, spacelike, and open-region null scalar gradients. Using a $2+1+1$ decomposition adapted to the causal character of the gradient, we derive the effective fluid variables associated with the proper kinetic gravity braiding contribution to the energy-momentum tensor. Unlike k-essence, where timelike scalar gradients generate perfect fluids while spacelike gradients lead to a simpler imperfect-fluid description, the braiding interaction introduces additional heat fluxes and pressure anisotropies. For timelike gradients, these consist of radial and tangential heat fluxes, whereas for spacelike gradients they become a radial heat flux together with mixed radial-tangential pressure anisotropies. These quantities are shown to depend exclusively on the normal fundamental scalars and the two-dimensional accelerations of the decomposition, despite the appearance of the full set of embedding and kinematic variables in the intermediate calculations. For open-region null gradients, the proper kinetic gravity braiding stress tensor has null-dust form. We further determine the Hawking-Ellis algebraic type of the effective stress tensor for all causal classes of the scalar field gradient, obtaining a complete geometrical classification of the effective matter content generated by proper kinetic gravity braiding. The timelike sector is of Type I for positive discriminant, Type II on the nontrivial discriminant hypersurface, and Type IV for negative discriminant. The spacelike sector has the same generic branches but, when the squared radial heat flux equals the squared mixed anisotropy, it also contains additional Type II and Type III degeneracies. The open-region null sector is of Type II for nonvanishing null-dust density, with the zero-density case reducing to the trivial vanishing stress tensor. Finally, the null, weak, dominant, and strong energy conditions further restrict the Type I and generic Type II sectors. The null energy condition already eliminates the Type III and Type IV branches and, in the spacelike gradient sector, every nonzero radial heat flux or mixed radial-tangential anisotropy. Thus, the standard energy conditions require the spacelike proper-braiding stress tensor to be diagonal, while in the timelike sector they bound the total heat flux.

We derive a class of vacuum regular black holes inspired by effective loop quantum gravity dynamics and extend the construction to asymptotically anti–de Sitter spacetimes. The derivation is based on a deparametrized Lemaître-Tolman-Bondi formulation, where an auxiliary dust field is introduced only to define an internal time and does not act as a matter source. In spherical symmetry, the dynamics reduces to a set of independent radial shells, giving rise to a factorized shell Hamiltonian and to a Birkhoff-type property: for a fixed reconstruction function and cosmological constant, the static geometry is uniquely determined by the mass. Within this framework, we establish the conditions for curvature regularity at the center and construct several regular black hole models with de Sitter cores and corresponding models with anti–de Sitter cores. We then study their thermodynamics in the extended phase space, using the Hawking-Page transition to compare the de Sitter- and anti–de Sitter-core branches and show that their quantitative differences arise from the deformation of the physical outer-horizon branch rather than from regularity alone.

We compute the gravitational fluxes and waveform for eccentric compact binaries including matter effects through adiabatic tidal interactions within the post-Newtonian approximation. The computations are performed at the relative 2.5PN order. Using the dynamics derived in Henry et al. (2025), we first derive the radiated energy and angular momentum, from which we deduce the equations describing the secular evolution of the orbital elements. We numerically solve for the secular dynamics for various systems. We find that the eccentric corrections to tidal terms induce a dephasing that could potentially be detectable in some regions of the parameter space of gravitational wave sources, especially for high enough initial eccentricity or mass ratio. Finally, we compute the amplitude of the strain, decomposed in spin-weighted spherical harmonics. Besides the memory contributions that are left for future works, we provide the amplitude modes containing the instantaneous, tail, and postadiabatic corrections expanded to the twelfth order in eccentricity. All relevant results are provided in the Supplemental Material. The expressions of the radiated fluxes and the secular evolution of orbital elements are valid for eccentricities up to 1, while the amplitude modes, due to the eccentricity expansion, are not valid beyond the Laplace limit $e_{\max }\simeq 0.663$.

GW200105 is the first gravitational wave detection to show moderate signs of eccentricity in a binary system involving a neutron star. This raises the need for waveforms that incorporate tidal effects on quasielliptic orbits. We tackle the problem of finite size effects within the post-Newtonian framework, including the mass-type quadrupole and octupole, as well as the current-type quadrupole deformations in the adiabatic approximation. The computations are performed at the second-and-a-half relative post-Newtonian order. We first derive the quasi-Keplerian parametrization of the conservative motion; we then express the radial separation and phase with their time derivatives in terms of the orbital frequency, the time eccentricity and the eccentric anomaly. To obtain these as functions of time, we invert the generalized Kepler equation while also discussing the convergence of eccentricity expanded results. We provide those results to the fourteenth order in eccentricity, which are not valid beyond the Laplace limit $e_{\max }\simeq 0.663$. Finally, we exploit the already known radiation reaction term of the acceleration in order to derive the secular and oscillatory evolutions of the orbital elements. The companion paper contains the derivation of the radiated fluxes and the amplitude modes of the strain. All relevant results are provided in the Supplemental Material.

We present the first lattice simulations of the nonlinear evolution after axion inflation by self-consistently incorporating currents arising from Schwinger pair production. The tachyonically amplified gauge fields trigger the growth of Schwinger currents, leading to universal values for the conductivity and magnetic field at the onset of strong backreaction and subsequent quenching of gauge-field production. We show that the Schwinger effect (prematurely) saturates gauge-field production, thereby diminishing the prospects of high-scale axion inflation magnetogenesis as a viable solution for blazar observations.

Scalar-induced gravitational waves (SIGWs) provide a powerful probe of inflationary dynamics on scales far smaller than those accessible to the cosmic microwave background and large-scale structure. In scenarios with a transient ultraslow-roll phase, the curvature power spectrum can be strongly enhanced on small scales, potentially generating an observable stochastic GW background. In this regime, scalar dynamics during inflation can become nonlinear, challenging the validity of standard perturbative predictions. Existing semianalytical calculations of SIGWs rely on the linear evolution of inflation fluctuations. In this work, we compute SIGWs from USR inflation using lattice simulations. We evolve the inflaton field nonlinearly during inflation and extract the curvature perturbation nonperturbatively, then simulate its postreheating horizon reentry by evolving the Newtonian potential linearly while retaining the full non-Gaussian structure of the initial conditions for the primordial fluctuations in the tensor source. For moderate non-Gaussianity, the semianalytical prediction captures the correct order of magnitude of the GW signal but receives important corrections. When inflationary non-Gaussianities are large, it can fail dramatically in both amplitude and spectral shape, independently of the overall size of the tensor power spectrum. Our results show that reliable predictions of SIGWs in such scenarios require nonperturbative control of the inflationary scalar dynamics. The code used for this work is available here.

We provide the first investigation of the solar production of symmetrons, a well-motivated class of screened scalar fields with density dependent couplings to the Standard Model, and their subsequent absorption in underground direct detection experiments. We compute the flux of symmetrons produced through photon conversion in the magnetic field of the solar tachocline, and constrain the resulting luminosity to not exceed 3% of the observed solar output. Even under the conservative assumption that production occurs only in the tachocline, this criterion yields robust astrophysical bounds on previously uncharted regions of symmetron parameter space, and predicts a keV-scale symmetron spectrum at Earth. We then derive the corresponding absorption signal in liquid xenon detectors, where symmetrons can interact with electrons through both conformal and disformal couplings. Using binned data from XENONnT, we obtain new direct-detection limits that are complementary to the solar luminosity constraint, further tightening the viable symmetron parameter space. Our results demonstrate that the Sun provides a testable, previously unexploited, source of symmetrons, and highlight that the interplay of astrophysical and laboratory searches offers a powerful strategy for probing screened scalar theories.

Hypothetical light scalar particles trigger the superradiant instability around spinning black holes (BHs), causing clouds of scalars to grow around the BH. In the presence of sufficiently strong particle self-interactions (characterized by the decay constant $f$), scalars are ejected from BH orbits, resulting in coherent, nonrelativistic emissions that continuously carry away the BH’s angular momentum. Parameters exist for which cloud growth is much faster, and scalar depletion is much slower, than the age of the Galaxy. This defines a distinct class of astrophysical sources of scalars, which we call BH scalar sirens; BHs that persistently emit scalars effectively forever. We compute the scalar background from the expected population of $N_{\mathrm{BH}}\sim {10}^8$ isolated stellar-mass BHs in the Milky Way, which are sirens for scalars in the mass range ${10}^{-13}-{10}^{-11}\mathrm{eV}$ and $f\lesssim {10}^{14}-{10}^9\mathrm{GeV}$. This provides a detection target independent of early-universe scalar production or cosmological initial conditions. The generated observable signals are up to two orders-of-magnitude larger than those expected from a misaligned cosmic scalar in this mass range. The energy spectrum of emitted scalars is distinctly broader and at higher velocities (up to $\sim {10}^{-1}c$) than that of virialized dark matter, and encodes the mass and spin distributions of the BH population. While stellar-mass Milky Way BHs are our primary target, our framework extends to supermassive, intermediate-mass and light BHs. Given the difficulty of directly observing populations of isolated BHs, scalar emissions offer a novel probe of these otherwise invisible objects, highlighting the potential for joint discovery between scalars and BHs, and broadly motivating searches for scalars over many orders-of-magnitude in mass.

The production of exotic hadrons $T_{cc}$ and $X(3872)$ in $pp$ collisions at $\sqrt{s}=7\mathrm{TeV}$ is compared using the parton and hadron cascade model together with the dynamically constrained phase-space coalescence model. In the simulation, the compact tetraquark state and the loose molecular state are formed in the partonic and hadronic levels, respectively. Our analysis of the transverse momentum spectra reveals a significant discrepancy between the compact state and the molecular states. Furthermore, the production asymmetry between $T_{cc}^{+}$ and $T_{cc}^{-}$ is investigated. Finally, the coalescence parameters are extracted from the calculated spectra to further characterize the emission source properties. These distributions are proposed as valuable criteria for distinguishing between these states and investigating their internal structures in experimental measurements.

Gravitational waves provide a unique probe of the strong-field regime of gravity, offering access to physics beyond the classical black hole paradigm. We explore how space-based observations of extreme-mass-ratio inspirals (EMRIs) by the Laser Interferometer Space Antenna (LISA) can be used to test for departures from the Kerr geometry, and in particular for the breaking of its axial and equatorial symmetries, as expected in quantum-gravity-inspired alternatives to Kerr black holes such as the fuzzball proposal. By introducing generic multipolar deformations encoding potential symmetry breakings and performing a systematic parameter estimation analysis, we forecast LISA’s ability to constrain such departures from the Kerr geometry in the strong-field regime. We show that EMRI signals with realistic signal-to-noise ratios can constrain several higher-order multipoles of the primary, opening a new observational window onto strong-field deviations from the Kerr geometry. In particular, we find that LISA can constrain generic nonaxisymmetric mass quadrupole deformations at the ${10}^{-4}–{10}^{-2}$ level and axisymmetric mass octupole deformations at the ${10}^{-1}-{10}^0$ level, providing concrete observational targets for strong-field deviations from the Kerr geometry, such as those that may arise in fuzzball and other exotic-compact-object scenarios. Our results demonstrate that precision measurements of EMRI waveforms will transform LISA into a powerful laboratory for fundamental physics and offer precise constraints on quantum-gravity-motivated models of compact objects.

We demonstrate how the two-dimensional gravity emerges within the “general relativity (GR) from renormalization group (RG)” program initiated in Refs. [1,2]. To achieve this, we consider a generic 2D conformal field theory (CFT) with a 3D holographic description, which we assume to be well described by pure Einstein-anti–de ${\mathrm{Sitter}}_3$ gravity in the bulk. We study the holographic RG flow for the 2D CFT action and show that the RG corrected action at an arbitrary energy scale contains a 2D scalar-tensor gravity theory. In the simplest case, the flow induces Jackiw-Teitelboim (JT) gravity, where the bulk radial lapse function seeds the dynamical dilaton field of the JT gravity. We show that the standard $\mathrm{T}\overline{\mathrm{T}}$ deformation of the 2D CFT is recovered as a special case in the Fefferman-Graham limit where the lapse is fixed. We further establish the robustness of the RG-induced gravity picture by verifying its consistency under holographic renormalization and by generalizing the result to a one-parameter family of boundary conditions. Our results provide a first-principles derivation of the JT gravity at a finite cutoff as an intrinsic manifestation of the holographic RG flow in a non-Fefferman-Graham gauge.

Modifications to general relativity can significantly alter the perturbative response of black holes, leaving imprints on quasinormal-mode spectra, waveform amplitudes and phases, and late-time tails. The parametrized beyond-Teukolsky framework was introduced to capture possible deviations from Kerr dynamics, but the ringdown has so far only been explored as an eigenvalue problem. We present the first time-domain implementation of this framework and perform ($2+1$)-dimensional scattering experiments with Gaussian wave packets. This approach provides the full linear evolution of the perturbation, from the initial prompt response through the ringdown and into the late-time regime. Using frequency-domain eigenvalue results as benchmarks, we find excellent agreement for low azimuthal numbers, while higher azimuthal numbers are affected by mode mixing, which limits the precision of the extracted modes. We further use the time-domain waveforms to estimate quadratic and mixed coefficients within the linearized modified-potential model, providing a diagnostic for the regime of validity of the linear approximation. Beyond mode frequencies, we show that the deformation parameters can strongly affect the ringdown amplitude and phase, with trends that can be understood from the near-horizon structure of the modified potential. We also analyze the late-time behavior, finding that near-horizon deformations leave the tail exponent unchanged but can substantially shift the onset of the power-law decay. These results demonstrate that time-domain evolutions provide a complementary and flexible framework for testing parametrized deviations from general relativity in black-hole perturbation theory.

We initiate the study of gravitational-wave lensing in the wave-optics regime within modified gravity. We consider a phenomenological setup in which the gravitational-wave amplitude obeys a curvature-coupled propagation equation. This framework reproduces the standard general relativity (GR) behavior in the geometric-optics regime, while leading to qualitatively different infrared dynamics. In particular, the usual argument implying that the amplification factor approaches unity in the zero-frequency limit no longer applies. This is due to the persistence of curvature-induced interactions in the infrared, which modify the natural propagation basis itself. As a result, the standard Fresnel treatment ceases to be valid at sufficiently low frequency. The correct infrared regime is instead controlled by an interacting static Green’s function, with a finite-frequency completion provided by a partial-wave formulation. We show that this structure admits an equivalent distorted-wave interpretation, in which the curvature interaction is absorbed into a dressed reference propagation basis, while the residual lensing effect is encoded in finite-frequency phase shifts. We further demonstrate that these phenomena admit a natural interpretation in the language of scattering amplitudes. Wave-optics lensing can therefore probe propagation-level departures from GR that remain entirely invisible in geometric optics.

Binary black hole (BBH) mergers detected via gravitational waves are addressing key open questions in astrophysics, cosmology, and fundamental physics. Our scientific conclusions rely on extracting accurate source parameters, for which we require accurate signal modeling. It is well known that current BBH waveform models need to be improved for high-mass-ratio, strongly precessing systems, and in this paper we provide a concrete illustration of this issue, showing that the degradation in model performance is substantially more severe than might have been anticipated. We present numerical relativity (NR) simulations of precessing BBH systems with a mass ratio of 18 and a dimensionless spin of 0.8 on the larger black hole (with the smaller black hole nonspinning), covering five values of spin misalignment. We assess the accuracy of state-of-the-art waveform models in this region of parameter space by computing the standard mismatch between the models and the NR waveforms. We find that all current waveform models often exhibit significant mismatches ($\gtrsim 0.1$), indicating poor performance in this regime. We also perform limited parameter estimation using a subset of state-of-the-art waveform models, injecting these NR simulations as signals into the three-detector LIGO-Virgo network. In some cases we find errors in mass measurements of over 100%, dramatically illustrating that substantial improvements are required in existing waveform models. The numerical simulations presented here will be valuable for calibrating future BBH waveform models in this region of parameter space.

We perform a search for binary black hole mergers with one subsolar mass (SSM) black hole and a primary component above $\sim 2M_{\odot }$ in data from the second observing run (O2) of the LIGO-Virgo detectors. Our analysis extends the parameter space explored by previous LIGO-Virgo Collaboration searches for binaries containing SSM components into a region of parameter space motivated by broad mass distributions of primordial black holes (PBHs) exhibiting a peak around $[2-3]M_{\odot }$, which can arise from the reduction of the equation of state during the QCD phase transition in the early Universe. Four candidate events are found passing a signal-to-noise ratio (SNR) threshold of 8 and a false alarm rate (FAR) threshold of 2 per year, although none are statistically significant enough to constitute a confident detection. Assuming a null result for the search, we derive PBH model-independent 90% confidence upper limits on the PBH merger rates by estimating the sensitive volume-time of the search using simulated gravitational-wave signal injections. We interpret these observational limits using a representative broad PBH mass function bearing imprints of the thermal history of the early Universe and considering both early and late PBH binary formation channels. The resulting constraints on the PBH dark-matter fraction, $f_{\mathrm{PBH}}$, depend on the assumed mass function and merger-rate prescription. For all considerations, the upper limits remain above $f_{\mathrm{PBH}}=1$, indicating the O2 data from LIGO-Virgo are not sensitive enough to place meaningful constraints within the assumptions of the PBH mass model and PBH binary mergers.

As the number of confident gravitational-wave detections grows, population-level hierarchical analyses face increasing computational costs. Dark-siren cosmological inference integrates over the localisation volume of each gravitational-wave source. To remain feasible without discarding information from the quieter but more numerous sources in the catalog, significant efficiency improvements are vital for analysis pipelines. In this work, we present an upgraded version of the cosmological inference pipeline gwcosmo, which leverages vectorisation on graphics processing units to process the entire gravitational-wave catalog in parallel with each iteration. This new implementation achieves a speed-up of $\sim {10}^3$ over the previous version, facilitating analyses of O5-like numbers of GW events on wall-clock timescales of hours. Our results demonstrate the scalability of the gwcosmo pipeline, specifically its ability to handle the increasing computational load of expanding event catalogs, positioning it as a vital tool for future advances in dark-siren cosmology.

The void probability function (VPF) is the likelihood of finding no tracers (galaxies or dark-matter haloes) within a given volume, and is sensitive to the large-scale matter distribution in the Universe. In this work, we investigate the VPF of dark matter haloes and galaxies using the quijote N-body simulations across a wide range of cosmological models, including both the standard $\mathrm{\Lambda }\mathrm{CDM}$ scenario and several well-motivated extensions. We examine in detail how the VPF responds to variations in cosmology, as well as to redshift ($z$), mass, morphology, and sample dilution, and compared the results with theoretical predictions from the geometric hierarchical (GH) and negative binomial (NB) models. We find that the VPF of haloes is sensitive to cosmology and halo mass, and follows the GH model at $z=0$, with the $\mathrm{\Lambda }\mathrm{CDM}$ model showing the smallest deviation, while the cosmology with massive neutrinos shows the largest deviation, likely due to neutrino free-streaming suppressing small-scale clustering and producing a smoother matter distribution. At higher $z$ and larger sample dilution, the VPF gradually departs from the GH model and trends toward the NB model. The VPF exhibits a dependency on the halo mass, with low-mass haloes showing the largest deviations from the GH model in the $\mathrm{\Lambda }\mathrm{CDM}$ cosmology, while intermediate- and high-mass haloes show the strongest deviations in the modified gravity scenario. In redshift space, the VPF shifts toward the NB model, with primordial non-Gaussianity producing the largest deviations, possibly due to enhanced redshift-space distortions. Furthermore, for galaxies, the VPF is dependent on the morphological type and underlying cosmology, with ellipticals following the GH model, while spirals follow the NB model. Lastly, we investigate the impact of cosmic variance using multiple $\mathrm{\Lambda }\mathrm{CDM}$ realizations and find that it introduces a non-negligible scatter in the VPF measurements. Overall, these results suggest that the VPF could be useful as a computationally efficient probe to distinguish extensions of the standard $\mathrm{\Lambda }\mathrm{CDM}$ model in upcoming large-volume galaxy surveys.