arXiv subjects

Fangli Quan

Publications and source records attributed to Fangli Quan.

3 recordsLinked to original sources

arXiv2026

Stationary scalar clouds around a rotating Kalb-Ramond BTZ black hole

We investigate the scalar clouds around a rotating Kalb-Ramond (KR) BTZ black hole under Robin boundary conditions. The clouds are obtained as stationary bound states at the superradiant threshold $\omega=m\Omega_H$, where the KR parameter, the rotation and the Robin boundary jointly determine their existence. It is shown that the KR parameter qualitatively changes the existence lines of clouds. For a nonpositive KR parameter, the lines remain monotonic, whereas for a positive KR parameter they can become nonmonotonic, so that a fixed boundary condition may admit clouds in disconnected regions of parameter space. Quasinormal modes (QNMs) and horizon fluxes are further used as consistency checks, confirming that the cloud solutions correspond to non-damping modes at the superradiant threshold where the energy flux changes sign. The KR parameter also shifts the critical Robin parameter at which the clouds exist. These results establish stationary scalar clouds as sensitive probes of the interplay between the Robin boundary conditions and KR gravity.

gr-qc↗

arXiv2026

Quasinormal modes and AdS/CFT correspondence of a rotating BTZ-like black hole in the Einstein-bumblebee gravity

We obtain exact expressions for the quasinormal modes (QNMs) of the massive scalar, fermionic and vector perturbations around a rotating BTZ-like black hole in the Einstein-bumblebee gravity. We find that the Lorentz symmetry breaking (LSB) parameter $\ell$ leaves its imprint only on the imaginary parts of the quasinormal frequencies and the corresponding perturbation field decays more slowly for a larger $\ell$, except for the left-moving quasinormal frequencies $\omega_L$ with positive mass and the right-moving ones $\omega_R$ with negative mass for the fundamental modes under the vector perturbation where the imaginary parts are independent of $\ell$. We also note that, regardless of the kind of perturbations, the real parts depend only on the angular quantum number, which are the same as those in the standard BTZ black hole. Furthermore, we investigate the AdS/CFT correspondence from the QNMs and observe that the expected universal relation for the left and right conformal weights ($h_L,h_R$) of the boundary operators dual to various fields still holds even for the BTZ-like black hole in the Einstein-bumblebee gravity. These results strongly support the AdS/CFT correspondence and could help us better understand the Einstein-bumblebee gravity with the Lorentz symmetry violation.

gr-qc↗

arXiv2025

Stationary scalar clouds around a rotating BTZ-like black hole in the Einstein-bumblebee gravity

We have studied stationary clouds of massive scalar fields around a rotating BTZ-like black hole in the Einstein-bumblebee gravity, by imposing the Robin type boundary conditions at the AdS boundary. We establish, by scanning the parameter space, the existence of \textit{fundamental} stationary scalar clouds ($i.e.$, the overtone number $n=0$). In particular, we observe that the Lorentz symmetry breaking parameter $s$ and the quantum number $k$ play an opposite role in determining scalar clouds, which indicates the existence of \textit{degenerate} scalar clouds. To illustrate the fact that scalar clouds may only be supported for the $n=0$ case, we have analyzed the impact of various parameters on scalar quasinormal modes. It is shown that the Lorentz symmetry breaking parameter $s$ does not change the superradiance condition, and superradiant instabilities only appear for the fundamental modes. Our work shows that the Lorentz symmetry breaking provides richer physics in stationary scalar clouds around black holes.

gr-qc↗