arXiv subjects

Yi-kun Li

Publications and source records attributed to Yi-kun Li.

5 recordsLinked to original sources

arXiv2026

Coherent Selection of Critical Kasner Response

A coherent wave component with extremely small initial self-energy can substantially change the first response of a contracting spacetime. We demonstrate this effect in Einstein--Maxwell--scalar theory with two commuting spacelike Killing fields. Along a critical family motivated by scalarized black-hole interiors, the estimated magnetic delay leaves time for longitudinal propagation to redistribute the incident field. Increasing a low-frequency component at fixed initial electromagnetic energy enhances the scalar response on one background and suppresses it on another. A calculation that propagates the field and its momentum, then their quadratic scalar and geometric sources, predicts this reversal before nonlinear evolution. At the first suppression comparison, the coherent profile error is $0.38\%$, against $46.9\%$ when cross terms are omitted. The selected response develops into a magnetic pulse with electric and scalar exchange. The critical geometry thus preserves incident coherence as information that predicts its first departure from a Kasner epoch.

gr-qc↗

arXiv2026

Optimal Extension Regularity at the McVittie Event Horizon

We determine the optimal local extension regularity of the future black-hole event horizon in the exact spatially flat McVittie solutions sourced by a positive cosmological constant and a barotropic fluid with constant equation-of-state parameter $w>-1$. Let $H_\infty$ be the asymptotic Hubble constant, $\kappa$ the surface gravity of the limiting black-hole root, and $p=3(1+w)H_\infty/\kappa$. Ingoing radial null geodesics reach the horizon in finite affine length. A parallelly propagated angular curvature component is asymptotic to $C s^{p-2}$, with $C\ne0$ and $s$ the remaining affine distance, which excludes every anchored $C^2$ extension for $0 \vartheta$. Every integer $p\ge2$ instead belongs to an analytic island and admits a real-analytic local extension. At the critical value $p=2$ the boundary Einstein endomorphism has a nonzero rank-one nilpotent part. The ratio of cosmological decay to horizon redshift therefore determines a sharp, arithmetic hierarchy of geometric regularity.

gr-qc↗

arXiv2026

Hair or a Boundary Source? Covariant Phase Space of a Static Type-I Black Hole

We study the two-parameter static type-I vacuum black hole recently obtained from an electromagnetic seed by a nonlinear solution-generating map. Its parameter $B$ changes dimensionless horizon geometry, yet the Komar mass variation at fixed asymptotic time is incompatible with the entropy variation. Using the Iyer--Wald, Barnich--Brandt, and Lee--Wald constructions, we derive the surface-charge one-form throughout the regular solution space and show that it has a nonzero curl. The same obstruction is measured by symplectic flux through the limiting Weyl boundary. A field-dependent normalization of the stationary Killing field supplies an integrating factor; the resulting energy $H=m/(1+B^2m^2)^{3/2}$ is uniquely selected by Schwarzschild mass normalization within this class. Homothetic scaling leaves the fixed-$G$ phase space two-dimensional because its tangent carries nonzero exact-symmetry charges. In Weyl coordinates, spatial infinity at finite mass is a closed surface of revolution. Its Brown--York canonical response reproduces the Lee--Wald flux pointwise. The semi-infinite annular source of the massless background emerges as a nonuniform limit of this surface. Finally, with $y=Bm$, the mechanics takes the global form $\text{d} M=T\text{d} S+\Psi_y\text{d} y$. Thus $B$ labels a genuine geometric deformation while its variation acts as external-source work in the Hamiltonian associated with fixed boundary time.

gr-qc↗

arXiv2026

Relativistic Tidal Transitions of Saturated Kerr Boson Clouds

Rotating black holes can bind ultralight bosons in macroscopic clouds whose level structure is swept by the tidal field of a binary companion. Existing estimates of the resulting resonant transitions have largely used hydrogenic wave functions, even where the cloud grows most efficiently and the Kerr geometry appreciably deforms its quasibound states. I compute tidal transition matrix elements on the numerically determined saturation branches of the $|211\rangle$, $|322\rangle$, and $|433\rangle$ clouds. The calculation combines Kerr quasibound modes, their relativistic bilinear normalization, and an adiabatic uadrupolar perturbation of the Kerr metric. Across five $\Delta m=-2$ channels, the relativistic matrix element differs from its hydrogenic value by as much as $21.67\%$. Corrections above $10\%$ persist when $99\%$ of the cloud lies within $7\%$ of the orbital separation. A component-resolved comparison attributes $78.7-82.5\%$ of the logarithmic change to the radial mode profile and $13.3-16.2\%$ to the bilinear normalization; the relativistic tidal geometry supplies a smaller additional correction. Exact Newtonian multipoles and an independent complex-contour construction confirm the quadrupole matrix elements. For resonances with intermediate Landau--Zener adiabaticity, the corrected matrix elements change the predicted cloud depletion by up to $13.7\%$. Relativistic cloud structure is therefore quantitatively important for binary histories that cross saturated-cloud resonances.

astro-ph.GA↗

arXiv2026

Model-Agnostic Population Inference for Gravitational-Wave Astronomy: From LVK to LISA

Inferring the intrinsic population of compact binary mergers is complicated by detector selection biases and measurement uncertainties. Traditional parametric methods are limited by the need to presuppose functional forms, introducing model-dependent biases. To overcome these limitations, we introduce an inference framework powered by deep generative modeling. We develop a flexible, data-driven population model using a Correlated Compound-Mixture Density Network. This architecture integrates mixture models to handle multimodality, Gaussian copulas for parameter dependencies, and a library of flexible marginal distributions. The network is trained to approximate the posterior distribution of the population's hyperparameters using amortized variational inference with Normalizing Flows on catalogs of gravitational-wave events. We demonstrate the framework's capabilities in two distinct regimes. First, using simulated catalogs of supermassive black hole binary mergers for the Laser Interferometer Space Antenna (LISA), we show that the method accurately recovers complex three-dimensional distributions and absolute merger rates from sparse datasets, effectively correcting for selection effects and measurement uncertainties. Second, we validate the framework on real observational data from the LIGO-Virgo-KAGRA GWTC-3 catalog, successfully inferring the population of stellar-mass binary black holes using an injection-based selection effect correction. Our results confirm that the method is robust, scalable, and applicable across different detector sensitivities and source populations.

astro-ph.IM↗