ALT Nonlinear tides couple stellar oscillations and reshape the gravitational wave (GW) signal from inspiralling binaries. We present hydrodynamic simulations of nonlinear tides in inspiralling neutron-star binaries and, within a mode-coupling model, derive a semi-analytic quadrupolar fundamental mode-frequency shift through second order in the tidal strength. The two approaches agree in the perturbative regime, but diverge at stronger tidal fields, where perturbation theory breaks down. In the late inspiral, nonlinear tides reduce the fundamental-mode frequency by ∼10% for equal-mass binaries and add a GW phase shift of O(1) radian beyond the linear tidal response. These effects make nonlinear tides a promising target for next-generation GW detectors.

ALT Radio pulsars emit highly polarized radiation whose polarization properties are commonly described by the Rotating Vector Model (RVM). In this work, we investigate the effects of gravitational light bending and parallel transport on the polarization profile of a pulsar in a hypothetical binary system with a black hole (BH) companion. We combine the RVM with numerical integration of null geodesics to calculate the polarization direction along the photon trajectory and model the orbital-phase-dependent variation of the observed polarization position angle (PPA). We consider both non-spinning and spinning black hole companions and include the evolution of the orbital geometry due to relativistic spin-orbit coupling. For a non-spinning black hole, the change in the observed polarization direction arises from the geometric shift associated with gravitational light bending. For a spinning black hole, frame dragging introduces an additional geometric shift, while parallel transport produces a

ALT In this paper, we introduce a metric describing rotating acoustic black holes in spherical coordinates. This formulation allows us to obtain exact analytical solutions of the massless Klein–Gordon equation governing scalar perturbations in the corresponding background spacetime. By imposing the appropriate boundary conditions, we derive an exact analytical expression for the quasibound state frequencies of the system. Quasibound states play a central role in the dynamics of black hole analog systems, as they characterize long-lived resonant modes trapped in the vicinity of the effective horizon. Their investigation provides valuable insights into wave propagation, mode stability, and energy confinement in analog spacetimes. Moreover, because acoustic black holes offer experimentally accessible realizations of horizon physics, the study of quasibound states may establish a direct connection between theoretical predictions and laboratory observations, thereby contributing to a deeper und

ALT We construct reflection-asymmetric thin-shell wormholes by joining a Schwarzschild exterior to its minimal geometric deformation, which shares the same mass and redshift function, so that the asymmetry is carried entirely by the gravitational-decoupling sector. The deformed side is a black hole sourced by a scalar field coupled to nonlinear electrodynamics, in its branch with a real scalar. We show that the total radial null energy of shell and bulk obeys an exact identity and becomes positive for a sufficiently strong deformation. The momentum flux across the shell equals the radial null-energy density of the bulk, and retaining it yields the linear stability condition in closed form. We prove that stability with a conventional shell response requires the bulk to violate the radial null energy condition at the throat; the deformation instead enlarges the stable domain and moves the transition radius inside the photon sphere. For a stationary extension built on Kerr, the junction is so

ALT We study the cosmological dynamics of a general class of viscous dark matter models using a dynamical system analysis. In the Eckart formalism, these viscous cosmologies are characterized by a dimensionless bulk viscous pressure ΩΠ≡ ΩΠ(Ωₘ), where Ωₘ is the matter density parameter. Our analysis demonstrates that a viable early radiation era requires the complete absence of viscosity, a proper matter-dominated epoch demands a small viscous pressure, and the only physically admissible late-time attractor is the cosmological constant-dominated fixed point; consequently, the background expansion must closely track standard ΛCDM evolution. We validate these general results using the power-law parameterization ΩΠ=-ξ̂₀ Ωₘˢ, where ξ̂₀ and s are real parameters; for s ≥ 1 and ξ̂₀ ≪ 1, the model reproduces the ΛCDM background, while for s < 1 the system encounters a past-time integration boundary where the dark matter density transitions into negative values and its viscous pressure evaluates to

ALT We study periodic orbits of charged particles in the equatorial plane of a five-dimensional (D=5) rotating Myers–Perry black hole (BH) immersed in a uniform magnetic field, and the gravitational waves emitted by these orbits in an extreme mass-ratio inspiral. All results are compared with the Kerr BH in the uniform magnetic field. We find that a charged particle is much more weakly bound to the D=5 dimensional BH, i.e. its energy at the innermost stable circular orbit is close to unity, 0.95–0.99, compared with 0.78–0.94 for the Kerr BH, and the depth of the potential well is several times smaller. As a result, the periodic orbits of the D=5 dimensional BH lie much closer to the separatrix. The magnetic field can make the azimuthal frequency of the orbit smaller than the radial one and produces loops in the orbits far from the BH. Using the numerical kludge method, we compute the gravitational waveforms for a compact object of 10M⊙ orbiting a BH of 10⁶M⊙. At the same magnetic field, th

ALT Under explicit and physically motivated assumptions, we identify a local-to-global thermodynamic mechanism that organizes several previously disconnected inequalities on black holes. We first focus on asymptotically flat, static, and spherically-symmetric black holes, and provide a unified thermodynamic perspective on various Penrose-like inequalities. We also discuss the generalizations in asymptotically Schwarzschild anti-de Sitter black holes/branes. In holographic settings, these bounds imply monotonic behavior of normalized thermodynamic quantities in the dual field theory. Notably, one central integrated inequality can be established directly under the NEC in general static planar symmetric asymptotically Schwarzschild anti-de Sitter black branes. Our purpose is not to claim a fully general proof of the proposed local bounds, but to expose a unified structural perspective connecting local thermodynamic constraints to global geometric inequalities. Establishing the local bounds be

ALT We identify the phase of a Bargmann invariant of two matter-wave interferometers as a quantum gravity signature that cannot be reproduced by any branchwise-definite classical gravitational field. For matter coupled linearly to linearized gravity, the interferometric coherence factorizes exactly into a conservative Newtonian phase, the characteristic functional of the graviton state, and a commutator phase. For Wigner-positive graviton states, the first two are classically reproducible; therefore, decoherence alone cannot certify that gravity is quantized. The Bargmann phase isolates the commutator, which is independent of the graviton state and of all Newtonian interactions and is bounded by which-path decoherence. For gravity, this radiation-reaction effect is sixty orders of magnitude below experimental reach, but trapped-ion analogs can test it at order unity.

ALT In this work, we construct an asymptotically conical regular black hole in four-dimensional nonpolynomial quasitopological gravity. Starting from a linear choice of the reduced function, which yields an asymptotically conical Schwarzschild-like solution, we introduce a nonlinear deformation that preserves the leading asymptotic cone while producing an exact black hole solution with a de Sitter core and finite curvature invariants. We further establish the corresponding black hole thermodynamics for both solutions within the Hamiltonian and Wald frameworks. The entropy contains rational and logarithmic terms in the regular model, and both solutions satisfy the first law of black hole thermodynamics.

ALT We study tensor perturbations and quasinormal modes (QNMs) of thick branes in f(R,T)=R+αT gravity. Starting from the background thick brane solutions, we derive the Schrödinger-like equation for gravitational perturbations and construct the corresponding effective potential. The effective potential exhibits a double-barrier structure whose properties depend on the model parameters. We analyze transmission spectra and find good agreement between resonance peaks and the real parts of the quasinormal frequencies. The parameters b and α mainly control the width and height of the potential barriers, respectively. QNMs are extracted using both time-domain evolution and direct integration methods, showing consistent results for low-lying modes. Higher overtones become increasingly difficult to extract due to stronger damping and numerical contamination. Our results indicate that f(R,T) corrections significantly affect both the effective potential and the quasinormal spectrum, providing a poss