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