Charged Scalar Field Perturbations Research Articles

Excited hairy black holes: Dynamical construction and level transitions

We study the dynamics of unstable Reissner-Nordstr\"om anti-de Sitter black holes under charged scalar field perturbations in spherical symmetry. We unravel their general behavior and approach to the final equlibrium state. In the first part of this work, we present a numerical analysis of massive charged scalar field quasinormal modes. We identify the known mode families - superradiant modes, zero-damped modes, AdS modes, and the near-horizon mode - and we track their migration under variation of the black hole and field parameters. We show that the zero-damped modes become superradiantly unstable for large RNAdS with large gauge coupling; the leading unstable mode is identified with the near-horizon condensation instability. In the second part, we present results of numerical simulations of perturbed large RNAdS, showing the nonlinear development of these unstable modes. For generic initial conditions, charge and mass are ransferred from the black hole to the scalar field, until an equilibrium solution with a scalar condensate is reached. We use results from the linear analysis, however, to select special initial data corresponding to an unstable overtone mode. We find that these data evolve to produce a new equilibrium state - an excited hairy black hole with the scalar condensate in an overtone configuration. This state is, however, unstable, and the black hole eventually decays to the generic end state. Nevertheless, this demonstrates the potential relevance of overtone modes as transients in black hole dynamics.

Time evolutions of scalar field perturbations in D-dimensional Reissner–Nordström Anti-de Sitter black holes

Reissner-Nordstr\"om Anti-de Sitter (RNAdS) black holes are unstable against the charged scalar field perturbations due to the well-known superradiance phenomenon. We present the time domain analysis of charged scalar field perturbations in the RNAdS black hole background in general dimensions. We show that the instabilities of charged scalar field can be explicitly illustrated from the time profiles of evolving scalar field. By using the Prony method to fit the time evolution data, we confirm the mode that dominates the long time behavior of scalar field is in accordance with the quasinormal mode from the frequency domain analysis. The superradiance origin of the instability can also be demonstrated by comparing the real part of the dominant mode with the superradiant condition of charged scalar field. It is shown that all the unstable modes are superradiant, which is consistent with the analytical result in the frequency domain analysis. Furthermore, we also confirm there exists the rapid exponential growing modes in the RNAdS case, which makes the RNAdS black hole a good test ground to investigate the nonlinear evolution of superradiant instability.

Charged scalar perturbations around a regular magnetic black hole

We study charged scalar perturbations in the background of a regular magnetic black hole. In this case, the charged scalar perturbation does not result in superradiance. By using careful time-domain analysis, we show that the charge of scalar field can change the real part of quasinormal frequency, but has little impact on the imaginary part of quasinormal frequency and the behavior of the late-time tail. Therefore, the regular magnetic black hole may be stable under the perturbations of charged scalar field at the linear level.

Quasinormal modes of regular black holes

Black hole quasinormal frequencies are complex numbers that encode information on how a black hole relaxes after it has been perturbed and depend on the features of the geometry and on the type of perturbations. On the one hand, the examples studied so far in the literature focused on the case of black hole geometries with singularities in their interior. On the other hand, it is expected that quantum or classical modifications of general relativity may correct the pathological singular behavior of classical black hole solutions. Despite the fact that we do not have at hand a complete theory of quantum gravity, regular black hole solutions can be constructed by coupling gravity to an external form of matter, sometimes modeled by one form or another of nonlinear electrodynamics. It is therefore relevant to compute quasinormal frequencies for these regular solutions and see how differently, from the ordinary ones, regular black holes ring. In this paper, we take a step in this direction and, by computing the quasinormal frequencies, study the quasinormal modes of neutral and charged scalar field perturbations on regular black hole backgrounds in a variety of models.

Dynamical perturbations and critical phenomena in Gauss–Bonnet AdS black holes

We investigate the perturbations of charged scalar field in 5-dimensional Gauss–Bonnet AdS black hole backgrounds. From the perturbation behaviors we obtain the objective picture on how the high curvature influences the spacetime perturbation and the condensation of the scalar hair. The high curvature effects can also be read from the linear response function such as the susceptibility and the correlation length, when the system approaches the critical point. We find that the Gauss–Bonnet term does not affect the critical exponents of the system and they still take the mean-field values.

Final fate of instability of Reissner-Nordström-anti-de Sitter black holes by charged complex scalar fields

We investigate instability of four-dimensional Reissner-Nordstr\"om--anti-de Sitter (RN-${\mathrm{AdS}}_{4}$) black holes with various topologies by charged scalar field perturbations. We numerically find that the RN-${\mathrm{AdS}}_{4}$ black holes become unstable against the linear perturbations below a critical temperature. It is analytically shown that charge extraction from the black holes occurs during the unstable evolution. To explore the end state of the instability, we perturbatively construct static black hole solutions with the scalar hair near the critical temperature. It is numerically found that the entropy of the hairy black hole is always larger than the one of the unstable RN-${\mathrm{AdS}}_{4}$ black hole in the microcanonical ensemble. Our results support the speculation that the black hole with charged scalar hair always appears as the final fate of the instability of the RN-${\mathrm{AdS}}_{4}$ black hole.

Quasinormal modes of Reissner–Nördstrom black hole surrounded by quintessence

We evaluate the complex frequencies of the normal modes for the charged scalar field perturbations around a Reissner–Nördstrom black hole surrounded by a static and spherically symmetric quintessence using third order WKB approximation approach. Quintessence decreases the oscillation frequency and increases the damping time of quasinormal frequencies. We studied the variation of quasinormal frequencies with charge of the black bole, mass and charge of perturbing scalar field and the quintessential parameters.