General Relativity and Quantum Cosmology Papers

ALT We prove the future C⁰-inextendibility of a broad subclass of ingoing Vaidya spacetimes with positive mass function satisfying the weak energy condition, building on methods introduced and developed by Sbierski for the Schwarzschild spacetime.

ALT The graviton self-energy -i [μν Σρσ](x;x') is the 1PI 2-point function of quantum gravity. It can be used to quantum-correct the linearized Einstein equation in order to infer quantum corrections to gravitational radiation and to the force of gravity. As long as the two points are non-coincident, the graviton self-energy does not need regularization at 1-loop order, however, solving the 1-loop effective field equations requires integrating [μν Σρσ](x;x') over x'μ, including x'μ = xμ. To facilitate this we employ dimensional regularization and BPHZ renormalization to compute the 1-loop contribution to the graviton self-energy, in pure quantum gravity, on de Sitter background, in the simplest gauge. We then solve the effective field equations to derive 1-loop corrections to the plane wave mode functions of gravitational radiation, and to the Newtonian potential. Although it seems possible to renormalize in such a way that the mode function shows no secular growth, the Newtonian potential

ALT We develop and validate a physics-informed neural network (PINN) framework for computing the tidal Love numbers of black holes directly from their perturbation equations. We consider static perturbations of the Kerr black hole, whose exact hypergeometric solutions provide a controlled benchmark for both the numerical solver and the extraction of the physical response. The framework combines exact enforcement of the horizon boundary conditions with an H²-Sobolev loss that incorporates derivatives of the differential-equation residual. The Love number is then obtained by extracting the asymptotic coefficients of the learned solution, without using the analytic connection formula. Across the tested scalar, vector, and tensor perturbations, the method recovers the finite dissipative response with relative errors below 10⁻⁵. Controlled comparisons show that the higher-derivative loss terms improve solution accuracy by orders of magnitude, while independent tests of the extraction procedure

ALT We study the de Broglie-Bohm quantum cosmology of a scalar field non-minimally coupled to a metric-compatible Riemann-Cartan geometry, comparing inflation with ekpyrotic contraction. The torsion trace is auxiliary and is eliminated algebraically before quantisation. The minisuperspace metric depends on the coupling F(φ) and a constant κ for an independent quadratic torsion term (κ=0 Einstein-Cartan, κ→∞ torsion-free). For every F, κ and potential this metric is conformally flat, so torsion acts only through the Einstein-frame kinetic function K(φ). Its curvature is therefore not a diagnostic of torsion, and the Laplace-Beltrami Wheeler-DeWitt equation, quantum potential and Bohmian trajectories are frame covariant. For a massless scalar the equation is solved exactly; in a two-packet state all 41 flux-weighted Bohmian trajectories bounce in the Einstein frame. In the Jordan frame the bounce at the symmetric event is independent of torsion and persists only for ξ<ξc (closed form); torsi

ALT Thermodynamic topology classifies black-hole equilibrium states through topological defects of an off-shell thermodynamic field, while quantum-corrected Hawking radiation can retain information about the quantum numbers of the emitted particle. Whether these two structures are connected has remained largely unexplored. In this work we investigate this question for a massive-gravity AdS black hole by combining arbitrary-spin zitterbewegung tunneling with generalized-uncertainty-principle corrections. We derive the particle-spin-dependent Hawking temperature, construct the corresponding channel-dependent effective entropy through the first law, and formulate the associated off-shell free energy and thermodynamic vector field. As reference sectors, we also analyze the Bekenstein-Hawking and exponentially corrected entropies. We find a clear separation between local and global thermodynamic topology. For the γ=-1 branch, a single positively wound defect persists, yielding W=+1, whereas for

ALT The light ring theorem states that four-dimensional stationary, axisymmetric, horizonless ultracompact objects (UCOs) possess light rings (LRs) in pairs, one of which is stable if the Null Energy Condition (NEC) holds in General Relativity (GR). The existence of a stable LR may trigger nonlinear spacetime instabilities, thereby raising questions about the viability of UCOs as long-lived black hole mimickers. We extend the LR existence and stability theorem beyond four-dimensional GR to modified gravity theories, in particular, f(R) gravity, scalar-tensor theories, and restricted Horndeski gravity, in (d ≥ 4) dimensional spacetimes. Our findings show that in four-dimensional modified gravities, the stability of LRs is governed by theory-specific coupling parameters in addition to the NEC. Consequently, a stable LR is not guaranteed to occur in certain parameter regimes. In higher dimensions (d>4), we confirm using topological arguments that LRs still emerge in pairs; however, the topolo

ALT We identify a cusp-type endpoint at which a finite radially stable region of solitonic boson stars disappears. Two fundamental radial zero-mode boundaries coalesce there, while the constrained quadratic stiffness and cubic coefficient vanish and the quartic coefficient remains finite and non-zero. The soft radial mode obeys Ω_soft∝ (σ_cusp-σ)¹/², revealing a divergent linear timescale at the endpoint. The same critical structure persists under the tested deformation of the scalar self-interaction.

ALT This work explores traversable wormhole solutions characterized by a quartic inverse-power density profile within f(T,τ) gravity. A specific inverse-power density profile, characterized by proportional to 1/r⁴ is introduced to establish the corresponding exact form of the shape function. The derived configuration exhibits all the necessary geometrical features of a traversable wormhole, such as throat formation, flaring-out behavior, and acceptable asymptotic characteristics. To gain further insight into the matter sector, we analyze the corresponding radial profiles of the energy density and pressure components. The throat region is characterised by negative radial pressure and null energy condition violation, both of which are relevant to the exotic matter content of the wormhole solution. To examine the lensing characteristics of the obtained spacetime, we employ the Gauss-Bonnet formalism to evaluate the gravitational deflection angle. Our findings indicate that the parameters γ an

ALT In this work we propose a holographic dark energy model inspired by the Ricci scalar R and non-metricity scalar Q. The infrared cutoff of the holographic dark energy is described by a combination of the Ricci scalar and the non-metricity scalar. Such a structure is very helpful because the evolution is entirely dependent on the universe's current characteristics rather than its previous or future characteristics. Additionally, the theory becomes more fundamental due to the application of invariants. We have built the model and examined its cosmological characteristics. The behavior of several cosmological parameters, including the density parameter, equation of state parameter, and deceleration parameter, is examined. It is observed that the holographic dark energy model may depict every cosmological epoch, beginning with radiation in the early universe, moving on to matter, and concluding with the dark energy-dominated period in later times. Depending on the parameter spaces selected,

ALT We construct a new family of exact spherically symmetric solutions in D-dimensional Brans-Dicke theory with n internal Ricci-flat spaces. The spacetime is assumed to be a product of a four-dimensional spherical sector and n Ricci-flat internal manifolds. By performing a conformal transformation to the Einstein frame, the problem is reduced to Einstein gravity with a minimally coupled scalar field, for which the exact solution is already known. Applying the inverse transformation to the Jordan frame yields explicit expressions for the metric and the Brans-Dicke scalar field, together with a generalized algebraic constraint on the exponents. The obtained solutions generalize the four-dimensional Brans solutions and the multidimensional solutions with Ricci-flat internal spaces. We analyze the causal structure of the four-dimensional section and derive the necessary condition for the surface R=L to be an event horizon, ν≡ |a+b+¹⁄₂∑ᵢ aᵢNᵢ|≥ 1. A Kretschmann-scalar analysis shows that, apar

ALT Mock data challenges need long stretches of colored Gaussian noise with a prescribed spectrum. The candidates are the crossfade of independently drawn windows that the standard gravitational-wave libraries implement, overlap-save finite-impulse-response filtering, autoregressive and autoregressive moving-average (ARMA) models, and the reproducible filter of PyCBC. One measure ranks them all: the covariance error against the target over the analysis band, evaluated from each generator's algebra; generated noise only checks the implementations. We also measure throughput, retained state and the cost of bit-exact regeneration. With the target continued smoothly below the band, the crossfade with windows of 256 s or more reaches an error below 10⁻³ on all eleven detector curves as tabulated, at about 4.7 million samples per second from a state of a few hundred bytes. An overlap-save filter is faster but needs tens of thousands of taps for an error of a few percent, and no tested autoregres

ALT The Moon provides a promising environment for gravitational-wave (GW) observations in the midband. The Laser Interferometer Lunar Antenna (LILA) combines a lunar deformation channel (LDC) and a geodesic deformation channel (GDC) to cover the midband. The LDC uses the Moon's resonant response to GW for the lower portion of the midband while the GDC measures displacement of suspended test masses to measure the latter. Radiation on the lunar surface can produce spurious signals through test-mass charging, momentum transfer, and thermoelastic deformation. We estimate these contributions for a notional 100 kg fused-silica optic using Geant4 transport, a finite-element electrostatic force map, and a spatial thermoelastic response kernel. Solar-minimum galactic cosmic rays and lunar albedo neutrons define a background case; a worst-day solar energetic particle spectrum (1989 solar flare conditions) defines an extreme, but rare, case. Aluminum-equivalent shielding from 50 to 1000 mils (1.27 to

ALT We investigate the total observed frequency shift of photons emitted by massive geodesic particles in circular orbits near the event horizon of bumblebee AdS black holes. The cosmological effects of the bumblebee field are investigated through dynamical equations governing the evolution and characteristic features of the Universe. In addition, the bumblebee field generates cosmological anisotropies by acting as a source of anisotropy and selecting a preferred spatial direction. We formulate the characteristic equations for the innermost stable circular orbit using the effective potential approach. Further analysis is devoted to establishing a functional relationship between the BH mass and the observed redshift and blueshift of photons emitted from the accretion disk. Finally, we study the shadow cast by the bumblebee AdS BH using the backward ray tracing process implemented in the Arcmancer code, where photon geodesics are initialized at the observers location and integrated backward

ALT In a binary black hole merger, the inspiral portion of the gravitational waveform corresponds to two distinct horizons orbiting each other, and the merger and ringdown signals correspond to the final horizon being formed and settling down to equilibrium. However, we still lack a detailed understanding of the relation between the horizon geometry in these three regimes and the observed waveform. In this thesis, we show that the well-known inspiral chirp waveform has a clear counterpart on black hole horizons, namely the shear of the outgoing null rays at the horizon. The shear behaves very much like a compact binary coalescence waveform with increasing frequency and amplitude, and the parameters of the system estimated from the horizon agree with those estimated from the waveform. We then track the source multipole moments of the dynamical horizons in simulations of several binary black hole mergers and calculate the corresponding Love numbers for axisymmetric modes. Unlike the (field)

ALT A thought experiment in the ER=EPR and related literature involves collecting the Hawking radiation of an old black hole, then collapsing it into a second, entangled black hole. In this short note, we examine the resources required by this idealized conversion. More specifically, we are interested in answering the question: how much external energy is needed to form the second black hole? Assuming a semiclassical bound on the information capacity of the newly formed black hole, we derive a conditional lower bound on external energy and a complementary constraint on correlations retained by the exterior degrees of freedom. We also distinguish entropy-level feasibility from the requirements for exact and approximate purification. We illustrate these requirements via a Page curve analysis.

ALT The dimensionality of spacetime is a fundamental property of nature, yet whether our observed four-dimensional spacetime is embedded in a higher-dimensional geometry remains experimentally unresolved. Gravitational waves (GWs) offer a direct probe of compact extra dimensions through the strong-field dynamics of binary coalescences. In this work, we investigate extra-dimensional modifications to GW generation within a compactified Kaluza–Klein framework. We derive the Newtonian conservative binary dynamics and the leading-order extra-dimensional correction to the GW energy flux and formulate the corresponding waveform modifications within the parameterized post-Einsteinian (ppE) framework. Combining these results with the previously derived 1PN amplitude correction arising from perturbations of the internal volume, we construct modified GW waveform templates for ground- and space-based detectors. To alleviate parameter degeneracies in GW parameter estimation, we combine the observed str

ALT noindent We develop a charge-matched thermodynamic framework for the regular rotating black-hole family underlying an exact model of Kerr formation. Since the Kerr endpoint already possesses a Cauchy horizon, hidden entropy is identified with the excess inner-horizon area relative to Kerr at fixed mass M and angular momentum J=Ma: Sexc=π[hc²-(r_-^Kerr)²], where hc is the regular inner-horizon radius and r_-^Kerr=M-√(M²-a²). Under regularity and interior-profile assumptions, we prove r_-^Kerr<hc<h and establish the sharp bound 0<Sexc<4πM√(M²-a²). The Schwarzschild limit yields Sexc=πhc², while Sexc=0 at the Kerr endpoint. The Kerr reference entropy satisfies S_+^Kerr+S_-^Kerr=4πM², so rotation redistributes its two-horizon contributions at fixed mass. For the time-dependent model, we derive exact evolution equations for the inner root and Sexc, interpreted as root-bookkeeping identities unless the roots are established as dynamical horizons. In the minimal N=1 trajectory, the apparent p

ALT The non-Hermitian nature of black hole quasinormal modes (QNMs) can give rise to remarkable spectrum instability. Such instability is naturally characterized by the pseudospectrum for the operator. However, conventional pseudospectrum analyses permit arbitrary operator perturbations that may not correspond to physically admissible modifications. In this work, we introduce the structured pseudospectrum into black hole perturbation theory. We construct two physically motivated perturbation spaces based on effective field theory and the Rezzolla–Zhidenko parametrization, and get their structured pseudospectra using two distinct norms. Our numerical results show that imposing physical constraints substantially reduces the accessible spectrum instability, especially for higher overtones. More importantly, at sufficiently small perturbation scales ε, the structured pseudospectrum around isolated QNMs exhibits approximately elliptical contours with preferred directions that depend on both the

ALT We numerically investigate the interior dynamics of D dimensional Reissner-Nordström (RN) black holes perturbed by a real scalar field. Strong perturbations destroy the null inner horizon and produce a spacelike singularity, whereas weaker perturbations preserve it with an areal radius that decreases as the perturbation amplitude increases. As the initial scalar field amplitude A approaches its critical value A, the inner horizon radius decreases continuously to zero. Near criticality, this radius obeys the power law rₛ∝|A-A|ᵞ. In four dimensions, different initial scalar field profiles and initial RN black hole charges yield nearly identical critical exponents, γ≃1/2, supporting the universality of the scaling law. For 4≤ D≤9, the numerical results are well described by γ≃1/(D-2). The corresponding scaling, |A-A*|∝ rₛᴰ⁻², indicates that the deviation of the initial parameter from its critical value is proportional to the area of the spherical cross section of the inner horizon.

ALT We investigate the fully nonlinear dynamics of Einstein-Maxwell-scalar black holes in the low-mass, near-extremal region of the solution space, which is difficult to access with conventional positive-energy perturbations. An independent phantom field is introduced as a controllable negative-energy channel, and its initial amplitude is varied while the remaining parameters of the initial data are held fixed. The phantom contribution is concentrated during the early-time infall and reduces the quasi-local mass in the black-hole region at fixed electric charge, thereby allowing the evolution to approach near-extremal configurations. Near a critical amplitude p∗, evolutions on both sides of the threshold enter the same long-lived scalarized intermediate stage before separating toward either a near-extremal Reissner-Nordstrom black hole or a nonextremal hairy black hole. The residence time near this intermediate stage obeys the logarithmic scaling law of Type I critical behavior, and the gr