General Relativity and Quantum Cosmology Papers

ALT The Laser Interferometer Space Antenna (LISA) is expected to observe gravitational-wave signals from massive black hole binaries, extreme mass ratio inspirals, and more. Despite the significant scientific potential, accurately extracting these signals from the data will only be possible if LISA's instrumental noise is understood: poor noise modelling will result in lost signals, biased parameter estimates, and incorrect astrophysical insights. Modelling LISA's instrumental noise is more challenging than its ground-based counterpart since the data is highly correlated, meaning that the noise covariance matrix can no longer be assumed diagonal in frequency and in the different data streams. In this work, we present an initial approach to perform non-parametric noise inference for LISA that requires no prior knowledge of the LISA observatory. By fitting the full noise covariance matrix with a combination of splines and inverse Lorentzians, we show that our model can estimate the power and

ALT We investigate the quasinormal modes (QNMs) and time-domain response of a massless, minimally coupled test scalar field on static, spherically symmetric covariant loop quantum black hole (cLQBH) backgrounds. Focusing on a phenomenological, Gaussian-localized holonomy profile, we obtain a localized deformation of the scalar effective potential containing both positive and negative parts. This provides a geometric realization of the bump effect, with the potential deformation and tortoise-coordinate mapping determined consistently by the same background. We characterize the deformation by its location, amplitude, and width, and study its effects using frequency-domain shooting and time-domain evolution, supplemented by matrix-pencil mode extraction and waveform reconstruction. The QNM spectrum exhibits spiral trajectories as the bump location varies, enhanced sensitivity of the overtones, and mode overtaking, whereby the branch continued from the first Schwarzschild overtone becomes long

ALT We present a calculation of the first-order metric perturbation arising from a point mass moving on a circular, equatorial orbit in Kerr spacetime. The metric perturbation is specifically aimed at meeting the requirements of second-order self-force theory: it is highly accurate; incorporates all contributions, including those associated with perturbations to the black hole's mass and angular momentum; is in Lorenz gauge near the worldline and in (near) Bondi–Sachs gauge at large radius; and can be efficiently evaluated across the entire exterior spacetime. The Lorenz gauge gives a well-understood singular structure at the particle, while the (near) Bondi–Sachs gauge ensures the asymptotic fall-off needed for an asymptotically flat second-order source. Our formalism reconstructs the metric from separable Teukolsky-type equations, decomposed into spin-weighted spheroidal harmonic modes and solved spectrally on hyperboloidal slices. The resulting (ℓ,m)-mode sums converge rapidly across mo

ALT We solve the frequency-domain, m-mode Teukolsky equation for the spin-weight s=-2 Weyl scalar ψ₄ sourced by a point mass on a circular, equatorial orbit around a Kerr black hole. The equation is posed on hyperboloidal slices that reach the event horizon and future null infinity, so that the physical (retarded) solution is selected by regularity alone, without imposing radiation conditions. The particle is treated with the m-mode puncture/effective-source scheme, and the resulting two-dimensional elliptic problem is solved with a four-domain pseudo-spectral method in which the equatorial symmetry is broken and handled by an even/odd decomposition of the field. We test the method for orbital radius r₀=10M and spins up to |a|/M=0.9, covering prograde and retrograde orbits. The energy fluxes to infinity agree with independent Black Hole Perturbation Toolkit results to ∼10⁻⁷ for the dominant modes and to better than 2×10⁻⁵ for all modes up to m=20 at moderate resolutions. The static m=0 mod

ALT We construct electrically charged black holes in Einstein's gravity coupled to the bosonic sector of the electroweak theory, focusing on static, spherically symmetric and asymptotically flat solutions, with the weak mixing angle fixed to its Standard Model value. Horizon regularity imposes a resonance condition relating the charged-vector frequency to the electromagnetic potential at the horizon, corresponding to the threshold of charged superradiance. A perturbative analysis further shows that nonextremal Reissner-Nordström black holes do not support regular, exponentially localized, spherically symmetric electroweak clouds satisfying such condition. Thus, the hairy solutions cannot emerge via a bifurcation from this electrovacuum family. Moreover, our numerical investigation reveals two apparently disconnected families of bosonic stars. Within the explored parameter space, the hairy black holes are connected to the strongly gravitating one.

ALT We show that the convergence region of the QNM representation of the retarded Green's function of the Kerr spacetime is set by complex-time bouncing singularities, as in our previous work for the Schwarzschild case. The main difference between Kerr and Schwarzschild is that there are two distinct QNM families, prolate and oblate, which have different convergence regions. We provide explicit analytical formulae for the bounce radii and corresponding convergence regions in Boyer-Lindquist coordinates. We also provide an analysis of convergence in the Reissner-Nordström spacetime.

ALT We prove the nonexistence of non-rotating and degenerate horizon components in the stationary, asymptotically flat, I⁺-regular, analytic vacuum spacetime. This result rules out the final case in the classification of stationary analytic black-hole spacetimes. Consequently, the stationary, asymptotically flat, I⁺-regular, analytic vacuum black hole uniqueness conjecture is settled affirmatively in full.

ALT We study circular null orbits, thermodynamic topology, and the holographic thermodynamic description of a four-dimensional magnetically charged AdS black hole in nonlinear electrodynamics. The background orbit structure is classified using Duan s phi-mapping construction and compared with the extraordinary electromagnetic characteristics. The latter defines an effective optical metric with an additional radial factor that modifies the orbit condition and introduces explicit dependence on the AdS radius. For four representative configurations, the local indices of the five isolated orbits are unchanged while their radii shift by up to 5.187 %. The background mass thresholds vary smoothly across sigma = 1/4 when the total mass is used, whereas the fixed-m0 parametrization is singular there. Regularity at the center requires sigma > 1 and m0 = 0. The thermodynamic analysis separates local stability indices from equilibrium coexistence: stable Gibbs-free-energy branches cross only in model

ALT We develop a reference-renormalized Jacobi-primitive Gauss-Bonnet formalism for finite-distance weak deflection of massive particles in static, spherically symmetric spacetimes. The construction uses the fixed-energy Jacobi metric associated with timelike geodesics and treats the radial curvature primitive as a quantity defined only up to an additive constant. Instead of fixing this constant by requiring the primitive to vanish at a circular timelike orbit, we subtract a reference Jacobi geometry at the same conserved particle energy and impose endpoint normalization on the curvature-density discrepancy. This gives a circular-orbit-free primitive representation of the Gauss-Bonnet curvature contribution while preserving the operational finite-distance definition of the bending angle through local source and receiver directions. We prove that the reference-normalized and circular-orbit-normalized prescriptions agree whenever both are admissible, since their primitives differ only by a c

ALT We develop a gauge-invariant teleparallel framework in which the universality of the gravitational coupling is relaxed for a scalar field, while the gravitational sector retains the form of the teleparallel equivalent of General Relativity. The non-universal interaction is encoded in a scalar-sector tetrad whose coupling to the universal translational gauge potential is controlled by a field-dependent gravitational charge. A Stückelberg completion preserves local translational gauge invariance, and we derive the gravitational, scalar-field, and Stückelberg equations, together with the antisymmetric constraint and their consistency relations. As a first application, we investigate homogeneous and isotropic cosmology, where the Stückelberg constraint provides a first integral governing the evolution of the non-universal coupling. In the kination-dominated regime, the standard stiff-fluid behavior is recovered asymptotically, whereas in the potential-dominated regime, accelerated expansio