arXiv subjects

Xi-Li Zhang

Publications and source records attributed to Xi-Li Zhang.

3 recordsLinked to original sources

arXiv2026

Causal Green function decomposition for quantum black hole seismology

The growing sensitivity of gravitational-wave detectors enables increasingly precise tests of black hole (BH) ringdown spectroscopy. BH quasinormal modes (QNMs) are, however, spectrally unstable: small near-horizon modifications can produce a drastically different QNM spectrum, while causality requires the prompt ringdown to remain BH-like until the reflected signal returns. Quantum BHs with substantial interior reflection provide a natural setting for this tension, yet the relation between their time-domain waveform and different QNM spectra still lacks a consistent picture. In this work, we systematically examine the time-domain Green function for quantum BHs, considering sources located outside and inside the light-ring potential barrier. By decomposing the Green function into causally distinct components and choosing the corresponding inverse-Laplace contours consistently, we clarify how the response is built from different sets of QNMs. We find that the quantum BH QNM reconstruction always faithfully describes the signal once the curved spacetime is probed, but its practical efficiency depends strongly on the evolutionary stage. Before interior reflection becomes relevant, we prove that this basis is formally equivalent to the BH QNM and tail expansions, with convergence properties sensitive to source location. At late times, the long-lived modes provide an efficient basis. Time-domain simulations confirm these results, providing a unified causal framework for BH spectroscopy and quantum BH seismology.

gr-qc↗

arXiv2026

Probing Boson Clouds with Supermassive Black Hole Binaries

Rotating black holes can generate boson clouds via superradiance when the boson's Compton wavelength is comparable to the black hole's size. In binary systems, these clouds can produce distinctive observational imprints. Recent studies accounting for nonlinearities induced by orbital backreaction suggest that if the binary forms at a large separation, resonance transitions can significantly deplete the cloud, minimizing later observational consequences except for very specific orbital inclinations. In this paper, we extend this framework to supermassive black hole binaries (SMBHBs), considering the influence of their astrophysical evolutionary histories. We find that, before entering the gravitational wave (GW) radiation stage, the additional energy loss channels can accelerate orbital evolution. This acceleration makes hyperfine resonant transitions inefficient, allowing a sufficient portion of the cloud to remain for later direct observations. We further discuss the ionization effects and cloud depletion occurring at this stage. Based on these theoretical insights, we explore how multi-messenger observations for SMBHBs can be utilized to detect the ionization effects of boson clouds by examining changes in the orbital period decay rate via electromagnetic measurements and variations in GW strain over a wide frequency band. Our findings reveal a complex dependence on the binary's total mass, mass ratio, and boson mass, emphasizing the significant role of astrophysical evolution histories in detecting boson clouds within binaries.

hep-ph↗

arXiv2025

Model-agnostic search of gravitational wave echoes in LVK data

Gravitational wave echoes offer a unique probe of the near-horizon structure of astrophysical black holes, beyond the standard "black hole spectroscopy." Theoretical waveform predictions, however, remain uncertain, motivating robust searches that avoid specific echo modeling. We present a model-agnostic search framework targeting long-lived quasinormal modes (QNMs) expected from strong interior reflection. By employing a generalized phase-marginalized likelihood that coherently combines data for each QNM across a detector network, our method enhances sensitivity to the signals. To handle real detector noise, we implement an optimized notching procedure to suppress instrumental spectral lines and refine the Bayesian parameter settings. We validate the performance of this framework using injection studies on O1 background data, demonstrating reliable signal recovery in realistic noise conditions. We then apply this method to three binary black hole merger events with high ringdown signal-to-noise ratios (SNRs): GW150914 from O1, GW231226 from O4a, and the recently reported O4 event GW250114. No statistically significant evidence for postmerger echoes is found. Consequently, we derive 90% upper limits on the network SNR and the average initial strain amplitude of the long-lived QNMs. These results provide model-agnostic constraints on late-time echoes from LVK data, complementing existing searches for other echo signatures.

gr-qc↗