General Relativity and Quantum Cosmology Papers

ALT It is commonly assumed that the mass of dark matter particles cannot be determined from their gravitational effects when dark matter behaves as collisionless matter. Here we show that extreme-mass-ratio inspirals observable by millihertz gravitational-wave observatories such as the Laser Interferometer Space Antenna (LISA) could measure the mass of ultralight dark matter particles in sufficiently dense dark matter spikes. The separation of scales between the two black holes allows ultralight dark matter to form a collisionless density spike around the massive primary while retaining wave effects in its interaction with the stellar-mass companion. We incorporate wave-dependent accretion and dynamical friction into relativistic inspiral waveforms and jointly infer the dark matter particle mass, spike normalisation and binary parameters from simulated LISA signals. For massive black holes at the low-mass end of the LISA population (M∼ 10⁵ M⊙), our forecasts show that particle masses spann

ALT We investigate how deviations from the Schwarzschild geometry affect the motion of massive test particles and the gravitational radiation associated with their periodic trajectories around a new improved Schwarzschild black hole. Periodic configurations are determined by examining the commensurability of the radial and azimuthal orbital frequencies. For representative trajectories, we numerically reconstruct the particle motion and calculate corresponding gravitational wave polarizations using the symmetric trace-free mass-quadrupole approach. By comparing these signals with their Schwarzschild counterparts, we assess how the modified spacetime geometry is encoded in the radiation. Our analysis shows that the parameters ξ and γ produce modest changes in the orbital configurations and their associated waveforms, providing a means of investigating the dynamical signatures of this BH model.

ALT Rotating black holes offer powerful probes of gravity, but constructing their geometries beyond vacuum general relativity remains challenging. Here we develop a unified framework for constructing stationary, axisymmetric deformations of Kerr from their tidal curvature and physical sources. As a demonstration, we obtain closed-form solutions for six higher-curvature interactions at leading order in the couplings and for generic subextremal spin, without slow-rotation expansions, numerical fitting, or mode decomposition. The solutions pass stringent checks against the field equations, previous mode-by-mode constructions, and known analytic predictions for horizon quantities. We find that the chirality of the interactions organizes the analytic structure of these solutions, a pattern that likely extends to a large class of purely metric higher-curvature theories. Our framework opens a systematic route to black-hole geometries in beyond-Einstein theories and perturbative astrophysical envi

ALT We study scalar and electromagnetic perturbations of a Schwarzschild black hole (BH) surrounded by a dark matter halo described by the King density profile. The lapse function can be expressed as 1-2[M+M_DM(r)]/r, where M_DM(r) is the halo mass enclosed within radius r; thus, the halo affects the geometry through its enclosed-mass function. We compute the quasinormal frequencies using the sixth-order WKB method and its Padé-improved version. Rewriting the lapse function in terms of the inverse hyperbolic sine avoids the severe numerical cancellations that arise when evaluating its high-order derivatives. For the configurations examined, the fundamental frequencies agree with those extracted from time-domain evolution to within 0.2%.The halo lowers both the oscillation frequency and the damping rate. The change of the real part is almost entirely accounted for by the halo mass enclosed by the photon sphere, and the additional decrease of the damping rate follows the ratio of the Lyapuno

ALT In this work, we investigate the geodesic dynamics and tidal force effects in neutral and electrically charged regular spacetimes inspired by T-duality. We first analyze the geometric properties of these solutions, including their regular central structure and horizon configurations, and show how the interplay between the T-duality scale ℓ₀ and the electric charge Q determines the transition between black hole and horizonless geometries. We then study the motion of massive and massless particles through the corresponding effective potentials, examining the existence and stability of circular orbits and the behavior of their characteristic radii. We further investigate the tidal forces experienced by observers in radial free fall, focusing on the behavior of the radial and angular components, their extrema and sign changes, and the location of these characteristic points relative to the horizon structure of the geometry. We show that the T-duality regularization renders the tidal forces

ALT We study a canonical scalar field coupled to isotropic triplets of Abelian one-forms and two-forms through scalar-dependent kinetic functions and a constant topological BF interaction. By retaining the lapse in the homogeneous reduction, we recover the Friedmann constraint and identify a sufficient domain in which all twelve physical modes have positive kinetic terms and luminal high-frequency propagation. A separate exponential model admits an accelerating mixed solution with a∝ t², nonzero asymptotic form fractions, and bounded normalized linear perturbations. For the Noether analysis, we choose a quadratic effective potential in flat minisuperspace coordinates and solve the zero-boundary determining equations. The canonical scalar potential is hyperbolic-squared or exponential, rather than a power law in the scalar field. The causal character of the potential coordinate separates three branches: Branch I admits a de Sitter limit, Branch II cannot sustain acceleration on regular futu

ALT We use the modified Newman–Janis algorithm to obtain the rotating “mother” black hole solution of the rotating Hayward-AdS black hole. We further derive the fundamental thermodynamic quantities of the “mother” black hole in the full unconstrained phase space (S,J,q,α,P), and impose the regularity condition M₁=q³/α to obtain the thermodynamic quantities of the rotating Hayward-AdS regular black hole. This order of operations gives a Hawking temperature identical to the surface gravity temperature and produces the correct response functions of the regular black hole. For P<Pc, the Hawking temperature T₂ possesses a local maximum and a local minimum, which divides the black hole into small, intermediate, and large black hole branches, and the P–V isotherms display oscillatory behavior characteristic of a liquid/gas phase transition. The small and large black hole branches are locally stable, whereas the intermediate black hole branch has negative heat capacity and is locally unstable. Inc

ALT We construct a Genesis scenario within the framework of a type-II minimally modified gravity. The background solution is past geodesically complete and approaches Minkowski spacetime in the asymptotic past. While the Hubble expansion rate grows, the matter sector satisfies the null-energy condition. Scalar perturbations are ghost-free and have no ultraviolet gradient instability, although the squared sound speed cℛ² becomes negative within a finite infrared region in the Fourier space for a finite time interval. Numerical evolution, including superhorizon growth, yields a nearly scale-invariant, slightly red-tilted scalar spectrum over a broad region of parameter space. The tensor spectrum is blue, with a strongly suppressed tensor-to-scalar ratio. Finally, using the matter fluctuation δχ, whose asymptotic normalization is regular, we find that the background-dependent cubic couplings vanish in the far past at fixed nonzero momenta. The surviving matter–graviton and graviton self-inter

ALT One of the central expectations of quantum gravity is the resolution of the curvature singularities predicted by General Relativity, potentially giving rise to effective black-hole geometries that are regular inside the horizon. We show that, for a very broad class of regular black holes including several known solutions, the quasinormal-mode spectrum in the large-overtone limit differs discontinuously from that of a Schwarzschild black hole, even when the regularization parameter is arbitrarily small. The real part of the quasinormal frequencies vanishes asymptotically, rather than approaching a nonzero constant, as generically occurs in General Relativity and other theories predicting black holes with curvature singularities. The asymptotic black-hole spectrum thus retains a distinctive imprint of singularity resolution. We establish these results analytically through a systematic formulation of the monodromy method and confirm them numerically. We interpret this phenomenon as a mani

ALT We formulate a description of self-gravitating Schrödinger–Poisson (SP) solitons in curved spacetime using a local inertial frame centered on the soliton. In the weak-field and non-relativistic regime, the effect of the background spacetime is incorporated into the SP equations through an effective tidal potential determined by the spacetime curvature. We apply this framework to a soliton moving along a circular equatorial geodesic around a Kerr black hole. The tidal field contains stationary and time-dependent quadrupolar components, which induce a deformation of the soliton and an associated mass quadrupole moment. We formulate the quadrupolar response in terms of the tidal deformability and the dimensionless Love number. We then estimate the gravitational radiation associated with the rotating deformed soliton and evaluate the corresponding characteristic strain for representative soliton sizes and orbital radii. A comparison with representative sensitivity curves of planned space-b

ALT We study the possibility of the formation of primordial black holes (PBHs) using an inflaton potential constructed by stabilizing all Kähler moduli employing both the perturbative and non-perturbative corrections in the large volume scenario in type-IIB/F string theory. We further introduce a small perturbation in one of the Kähler moduli that modifies the existing potential in the field space. The effective correction in the moduli space is made by introducing a localised Gaussian bump, which induces an ultra-slow-roll feature in the inflaton potential during the early cosmological inflation. The evolution of the amplitude of the curvature power spectrum is solved numerically by using the Mukhanov-Sasaki equation, with Bunch-Davies initial conditions. The inclusion of the Gaussian bump produces a sustainable enhancement in the amplitude of curvature power spectra around k∼ 1.12 × 10⁹ Mpc⁻¹ for the formation of PBHs. The abundance of PBHs (f_PBH) is calculated using the Press-Schechter

ALT We investigate the hydrostatic equilibrium and global structure of neutron stars within symmetric teleparallel gravity, where gravitational interactions are mediated by the non-metricity scalar Q. Working within the metric-affine formulation, we adopt the regular, constant-Q branch (Q = Q) of f(Q) gravity, which preserves regularity at the stellar centre while maintaining explicit dependence on the non-linear functional form through f(Q₎ and its derivatives. We propose three novel non-linear f(Q) extensions: (i) a Born-Infeld-inspired model, (ii) a Hu–Sawicki analogue, and (iii) a Tsujikawa-inspired model. Incorporating state-of-the-art realistic unified equations of state, namely GPPVA(DD2) and SLy4, we numerically solve the modified Tolman-Oppenheimer-Volkoff equations and evaluate stellar stability via the Harrison-Zel'dovich-Novikov criterion. The Born-Infeld and Hu-Sawicki analogues smoothly recover the general relativistic limit as their control parameters increase, predicting st

ALT By treating black-hole states as topological defects in thermodynamic parameter space, we investigate a static, asymptotically flat magnetic black holes in Einstein gravity coupled to causal nonlinear electrodynamics. Using the generalized off-shell free energy and Duan's φ-mapping topological current theory, we analyze the physical single-horizon sector in the canonical ensemble. We identify four representative defect-curve profiles, including realizations of the conjectured W⁰⁺↔¹⁻ class and W̅¹⁻ subclass, as well as a new thermodynamic topological subclass, W̅⁰⁺↔¹⁻. This new subclass features paired generation and annihilation points, with unstable innermost and outermost branches. As the auxiliary inverse temperature increases, the system evolves from two equilibrium states to three and then back to one, with an unstable small-black-hole defect entering through the physical lower boundary and changing the global topological number from W=0 to W=-1. This boundary-induced change signa

ALT This paper investigates the greybody factor and Joule-Thomson expansion of deformed Schwarzschild-AdS black hole models. We constructed the Klein-Gordon equation into a Schrödinger-like wave equation using tortoise coordinates and derived the exact effective potential. Also, we analyzed its behavior under varying physical parameters, including deformation parameters, mass and angular momentum. In this case, our results illustrate that increasing the deformation parameter enhances the effective potential, significantly impacting the absorption and scattering of massless scalar fields. It is noted that the Schwarzschild black hole effective potential is greatly increased when the deformation parameter is present. Near the event horizon, we found that waves behave differently, with higher-frequency waves more easily penetrating potential obstacles and lower-frequency waves bouncing off them. Furthermore, we investigated the thermodynamic characteristics of black holes using the Joule-Thom

ALT Gravitational-wave (GW) observations of binary black holes provide a powerful probe of general relativity (GR) in the strong-field regime. In effective field theory (EFT) extensions of GR, higher-curvature operators modify the binary dynamics and introduce corrections to the inspiral phase. In this work, we consider two parity-even cubic-curvature couplings and one quartic-curvature coupling, whose leading phase corrections enter at 5PN, 6PN, and 8PN order, respectively. We incorporate these corrections into the individual multipoles of the SEOBNRv5HM_ROM waveform using the flexible theory-independent framework, allowing higher-order modes and the full inspiral-merger-ringdown signal to be used in the analysis. We first perform a Fisher-matrix analysis of 92 binary-black-hole events selected from a parent sample of 273 events in the public LIGO-Virgo-KAGRA catalogs. GW230627₀15337 provides the tightest forecast constraints on all three EFT couplings and is therefore selected for a full

ALT A causal set is a locally finite partially ordered set. Causal set theory proposes such discrete structures as a basis for spacetime physics. Connecting this description with continuum physics requires recovering the geometric quantities used in general relativity and controlling the errors introduced by discreteness. Here, with dimension and sampling density specified, we construct approximate normal coordinates, estimate parallel transport, and recover the full Riemann tensor from causal order and element counts. For samples embedded in a fixed smooth spacetime and satisfying stated uniform counting assumptions, we prove a uniform curvature error bound that tends to zero as the sampling density increases.

ALT We study the shadows of a charged rotating de Sitter solution in fourth order conformal Weyl gravity (CWG) immersed in plasma and analyze the joint charge-plasma constraints. Our main goal is to distinguish observational effects caused by the dispersive plasma environment from those caused by the underlying gravitational theory. Within a separable Hamilton-Jacobi plasma model, we derive the radial and angular photon potentials, the equatorial finite-distance deflection angle, and the finite-observer shadow boundary due to the asymptotically non-flat nature of the CWG spacetime. Our results separate two effects. Increasing the plasma strength generally reduces the shadow radius, the signed deflection angle, and the energy emission peak in both CWG and GR. Charge (q) produces a stronger theory dependence: for the representative parameters studied, increasing q enlarges the CWG shadow but reduces the GR shadow. The lensing behavior independently supports the geometry-dependent response fo

ALT We present the first study of coexisting Vainshtein and Chameleon screening in cosmic structures. Screening hides fifth forces locally, keeping modified gravity viable. Realistic dark-energy models can activate several mechanisms at once, yet this interplay has been overlooked. We find that (i) the Chameleon resolves the long-standing Galileon void pathology; (ii) it suppresses or eliminates the Vainshtein radius around massive sources; and (iii) the Vainshtein term shrinks the Chameleon's screened core. These effects reshape the observable signatures central to cosmological tests of gravity.

ALT This Letter investigates gravitational-wave tests of the horizon area law. Although they provide a striking consistency check of general relativity (GR), these tests rely on models that assume GR, making their interpretation inherently model dependent. We show with a specific example—simulations of merging boson stars—that exotic compact objects can mimic merging black holes and pass an area-law test at a confidence as high as ∼ 92% despite not even having event horizons.

ALT In this study, we investigate the gravitational particle production (GPP) as a natural reheating channel in time-dependent backgrounds. We focus on reheating in an inflation-kination background. To maintain generality across inflationary models, we use a continuous scale-factor function that produces this transition and has been proposed in the literature. In this scenario, the gravitational reheating channel arises from the gravitational excitation of a superheavy spectator scalar field with Ricci-matter gravitational coupling. Besides all the perturbative approaches, a recently proposed non-perturbative one that uses the notion of the adiabatic vacuum has also been applied to the case of superheavy particles. Although the effect of the mass of the field on the reheating temperature has been investigated, the impact of the non-conformal values of the gravitational coupling constant on the GPP rate is not considered. Hence, we modify the non-perturbative approach in such a way that bot