arXiv subjects

Libo Xie

Publications and source records attributed to Libo Xie.

7 recordsLinked to original sources

arXiv2025

Quasinormal modes of Schwarzschild-de Sitter black holes in semi-open systems

We study perturbations of Schwarzschild-de Sitter black holes in semi-open systems by using the Heun functions. For the semi-open system, a partially reflective wall is added around the event horizon. Three aspects of this model are investigated, namely the quasinormal mode (QNM) spectra, the greybody factor (GF), and the exceptional point (EP). For the QNM aspect, we identify three distinct behaviors as the frequency-independent reflectivity $\mathcal{K}$ increasing. The first-type modes approach the real axis and form long-lived quasi-bound states. The second-type modes move toward but do not reach the real axis and retain a finite decay rate. The third-type modes eventually lie on the imaginary axis becoming purely decaying modes. For the GF aspect, GFs exhibit strong oscillations controlled by the distance between the potential and the reflective wall with a real constant reflectivity. In contrast, a Boltzmann-type reflectivity produces only small corrections. Finally, by promoting $\mathcal{K}$ to a complex parameter, the modified boundary conditions give rise to a second-order EP. Parameterizing the vicinity of such EP, we observe the mode exchange phenomenon, and the deviation of spectra scale with the square root of the deviation of the parameter, as predicted by a Puiseux series expansion.

gr-qc↗

arXiv2025

Waveform stability for the piecewise step approximation of Regge-Wheeler potential

By interpreting the difference between the original Regge-Wheeler potential and its piecewise step approximation as perturbative effects induced by the external environment of the black hole, we investigate the stability of Schwarzschild black hole time-domain waveforms. In this work, we employ the Green's function method under the assumption of an observer at spatial infinity to obtain the waveform. For two cases in which the initial Gauss bump near the event horizon or at spatial infinity, we derive analytic expressions for the corresponding waveforms. Our results demonstrate that the waveform is indeed insensitive to tiny modifications of the effective potential, thereby confirming its stability. More importantly, we find that broader initial bumps imprint the influence of small environmental modifications more clearly on the waveform, which may provide theoretical guidance for probing the exterior environment of black holes.

gr-qc↗

arXiv2025

Spectrum instability and greybody factor stability for parabolic approximation of Regge-Wheeler potential

We investigate the stability of QNM spectra and greybody factors in the Schwarzschild black hole by approximating the Regge-Wheeler potential with a piecewise parabolic form and treating the deviation as a perturbation. We find that QNM spectra are sensitive to small perturbations, while greybody factors remain stable. This piecewise parabolic approximated potential gives rise to the long-lived modes whose imaginary parts remain close to zero and decrease slowly with overtone number increasing. The reflection coefficient shows distinct resonance feature in the high-frequency regime that are absent in the original R-W case. For the calculation of greybody factors, we employ an analytic method based on transfer matrix technique, and this approach can also be effectively used in other effective potential cases.

gr-qc↗

arXiv2024

The stability of the greybody factor of Hayward black hole

In this study, we investigate the stability of the greybody factor of Hayward black holes by adding a small bump to the effective potential. Since the greybody factor depends on frequency, we introduce the $\mathcal{G}$-factor and $\mathcal{H}$-factor to quantitatively characterize its stability. We study the stability of the greybody factor within the equal amplitude method and the equal energy method, respectively. Here, the equal amplitude method can be directly imposed by fixing the amplitude of the bump, while the equal energy method requires a physical definition of the energy of the bump with the assistance of hyperboloidal framework. For both methods, when the location of the bump is close to the event horizon of the black hole, and the closer it is to the peak of the original potential, the larger are $\mathcal{G}$-factor and $\mathcal{H}$-factor, and they are bounded by the magnitude of the amplitude or the energy. More importantly, for the equal amplitude method, two factors tend to a specific value as the location of the bump increases. In contrast, for the equal energy method, two factors converge to zero as the location of the bump increases. Notably, the $\mathcal{G}$-factor and the $\mathcal{H}$-factor are insensitive to the regular parameter of Hayward black hole. Therefore, our results indicate that the greybody factor is stable under specific perturbations.

gr-qc↗

arXiv2024

The pseudospectrum and spectrum (in)stability of quantum corrected Schwarzschild black hole

In this study, we investigate the pseudospectrum and spectrum (in)stability of quantum corrected Schwarzschild black hole. Methodologically, we use the hyperboloidal framework to cast the quasinormal mode (QNM) problem into an eigenvalue problem associated with a non-selfadjoint operator, and then the spectrum and pseudospectrum are depicted. Besides, the invariant subspace method is exploited to improve the computational efficiency for pseudospectrum. The investigation into the spectrum (in)stability entails two main aspects. On the one hand, we calculate the spectra of the quantum corrected black hole, then by the means of the migration ratio, the impact of the quantum correction effect on the Schwarzschild black hole has been studied. The results indicate that the so-called ``migration ratio instability" will occur for small black holes with small angular momentum number l. In the eikonal limit, the migration ratios remain the same for each overtone. On the other hand, we study the spectrum (in)stability of the quantum corrected black hole by directly adding some particular perturbations into the effective potential, where perturbations are located at the event horizon and null infinity, respectively. There are two interesting observations under the same perturbation energy norm. First, perturbations at infinity are more capable of generating spectrum instability than those at the event horizon. Second, we find that the peak distribution can lead to the instability of QNM spectrum more efficiently than the average distribution.

gr-qc↗

arXiv2022

Higher dimensional Reissner-Nordstr\"{o}m black holes supporting static scalar shells

We analytically study scalarization of higher-dimensional charged Reissner-Nordstr\"{o}m (RN) black hole. It is shown that static massive scalar field which is non-minimally coupled to Gauss-Bonnet invariant can be supported by higher-dimensional black hole in super-critical charge regime $Q/M\ge \bar{C}_d$ with $Q, M$ charge and mass of the black hole and $\bar{C}_d$ some unitless spacetime dimension-dependent quantity. Moreover, we show that the static massive scalar shell can be quite thin in the large mass regime $\mu M^{\frac{1}{d-3}}\gg 1$ with $\mu$ mass of the scalar field.

hep-th↗

arXiv2022

Scalar-hairy Lovelock gravity respects zeroth law

We study the zeroth law for Killing horizon in scalar-hairy Lovelock gravity, and show that the surface gravity of a general Killing horizon in the scalar-hairy Lovelock gravity is constant, provided that the dominant energy condition is obeyed by the matter field.

gr-qc↗