Charged Scalar Perturbations Research Articles

Superradiant instability of charged extremal black holes in Einstein-Born-Infeld gravity

We study charged scalar perturbations of charged extremal black holes in Einstein-Born-Infeld theory. Our numerical results indicate that these black holes all suffer from superradiant instability by the unstable quasi-bound states, regardless how small the coupling constant is. We therefore provide a new example that the superradiant stability of the Reissner-Nordström black hole is a fine-tuned result, as in the case when it is embedded in the STU supergravity model. The work is also motivated by the weak gravity conjecture since at the linear coupling constant level, the theory belongs to a subsect of four-derivative corrections in the effective field theory. Our results appear to support the notion that the black holes do decay when gravity is weaker by the correction, but the decaying halftime requires nonlinear effects and cannot be seen at the level of linear coupling constant. The full nonlinear effects also indicate that the black holes can decay even when gravity is stronger.

Stability and pair production of scalars in the charged Einstein–ModMax black hole spacetime

This study has established the stability of Reissner–Nordström black holes within a specific parameter range against charged scalar perturbations. Additionally, the near-extremal Reissner–Nordström black holes exhibit a phenomenon known as the Schwinger effect for black holes, involving the production of charged scalar particles. This paper explores the stability and Schwinger effect in the context of static charged black holes within the Einstein–ModMax theory. Our approach closely aligns with the existing literature methods. We aim to investigate how the nonlinearity inherent in the theory may impact both the stability regime and the rate of charged scalar pair production by the black hole.

Superradiance instabilities of charged black holes in Einstein-Maxwell-scalar theory

We study time evolutions of charged scalar perturbations on the background of a charged hairy black hole, in which the perturbations can be governed by a double-peak effective potential. By extracting quasinormal modes from the waveform of scalar perturbations, we discover that some quasinormal modes, which are trapped in a potential well between two potential peaks, can be superradiantly amplified. These superradiant modes make the hairy black hole unstable against charged scalar perturbations. Moreover, it is found that the superradiant modes arise from the competition between the superradiant amplification caused by tunneling through the outer potential barrier and the leakage of modes through the inner potential barrier into the black hole.

Superradiant instability of dyonic Reissner–Nordström black holes

We investigate the superradiant instability of dyonic Reissner–Nordström (dRN) black holes with two charges under an electrically charged massive scalar perturbation. Two conditions for possessing a trapping well are obtained from analyzing asymptotic scalar potential and far-region wave functions. It is clear that the superradiant instability is not allowed in the dRN black holes because the conditions for a trapping well are not compatible with the superradiance condition.

Quasinormal modes of the Einstein-Maxwell-aether black hole

We study the quasi-normal modes of the charged scalar perturbations in the background of the Einstein-Maxwell-aether black hole through three methods (WKB method, continued fraction method, generalized eigenvalue method). Then we propose the specific treatment for the generalized effective potential with $\omega$-dependence and the complete procedure of transforming calculation continued fraction method into finding the zero point of the corresponding complex function numerically. These methods are valid because the results from different methods are consistent. We also investigate the allowed region of the second kind aether black hole among the system parameters ($c_{13},c_{14},Q$). Finally we show the existence of quasi-resonances of massive perturbation for Einstein-Maxwell-aether black hole even with large aether parameter.

Quasinormal oscillations and late-time tail of massless scalar perturbations of a magnetized black hole in Rastall gravity* *Supported by the National Natural Science Foundation of China (NNSFC) (11805166, 11925503, 12175076). We also gratefully acknowledge the financial support from Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro

In this study, we investigate the quasinormal mode and late-time tail of charged massless scalar perturbations of a black hole in generalized Rastall gravity. The black hole metric in question is spherically symmetric, accompanied by a power-Maxwell field surrounded by a quintessence fluid. We show that the massless scalar field, when dressed up with the magnetic field, acquires an effective mass, which significantly affects the properties of the resultant quasinormal oscillations and late-time tails. Specifically, the quasinormal frequencies become distorted and might even be unstable for particular spacetime configurations. Additionally, the exponent of the usual power-law tail is modified according to the modification in the structure of the branch cut of the retarded Green's function. In particular, as the effective mass is generated dynamically owing to the presence of the magnetic field, we may consider a process through which the field is gradually removed from the spacetime configuration. In this context, while the quasinormal oscillations converge to the case of massless perturbations, we argue that the properties of resultant late-time tails do not fall back to their massless counterpart. The relevant characteristics are investigated using numerical and analytic approaches.

Superradiant instability in slowly rotating Kerr–Newman black holes

In this paper, we study the superradiant instability of slowly rotating Kerr–Newman (sKN) black holes under a charged massive scalar perturbation. These black holes resemble closer the Reissner–Nordström black holes than the Kerr–Newman black holes. From the scalar potential analysis, we find that the superradiant instability is not allowed in the sKN black holes because the condition for a trapping well is not compatible with the superradiance condition. However, the rate of energy extraction might grow exponentially if the sKN black hole is placed inside a reflecting cavity. Finally, we obtain two conditions for the trapping well to possess quasibound states in the sKN black holes by analyzing asymptotic scalar potential and far-region wave functions.

Six-dimensional non-extremal Reissner-Nordstrom black hole, charged massive scalar perturbation and black hole bomb

The superradiant stability of higher dimensional non-extremal Reissner-Nordstrom black hole under charged massive scalar perturbation is analytically studied. We extend our previous studies of four- and five-dimensional non-extremal Reissner-Nordstrom black hole cases to six-dimensional case. By analyzing the derivative of the effective potential with an analytical method, we find that no potential well exists outside the outer horizon of the black hole for the superradiant scalar modes. This means that there is no black hole bomb for the system consisting of six-dimensional Reissner-Nordstrom black hole and charged massive scalar perturbation and the system is superradiantly stable.

Conditions for superradiant instability of the Kerr-Newman black holes

We find two conditions for superradiant instability of Kerr-Newman black holes under a charged massive scalar perturbation by analyzing asymptotic scalar potential and far-region wave function. Actually, they correspond to the condition for getting a trapping well. Also, we obtain the conditions for superradiant stability of Kerr-Newman black holes which states that there is no trapping well. The analysis is applied to Kerr black holes to find a condition for superradiant instability.

Revisiting superradiant stability of Kerr–Newman black holes under a charged massive scalar

We revisit the superradiant stability of Kerr–Newman black holes under a charged massive scalar perturbation. We obtain a newly suitable potential which is not singular at the outer horizon when a radial equation is expressed the Schrödinger-type equation in terms of the tortoise coordinate. From the potential analysis, we find a condition for the superradiant stability of Kerr–Newman black holes.

No black hole bomb for D-dimensional extremal Reissner–Nordstrom black holes under charged massive scalar perturbation

The superradiant stability of asymptotically flat D-dimensional extremal Reissner–Nordstrom black holes under charged massive scalar perturbation is analytically studied. Recently, an analytical method has been proposed by the author and used to prove that five and six-dimensional extremal Reissner–Nordstrom black holes are superradiantly stable under charged massive scalar perturbation. We apply this analytical method in the D-dimensional extremal Reissner–Nordstrom black hole case and prove that there is no black hole bomb for D-dimensional Reissner–Nordstrom black hole under charged massive scalar perturbation and the system is superradiantly stable.

Higher-dimensional non-extremal Reissner-Nordstrom black holes, scalar perturbation and superradiance: An analytical study

The superradiant stability of asymptotically flat higher dimensional non-extremal Reissner-Nordstrom black holes under charged massive scalar perturbation is analytically studied. We extend an analytical method developed by one of the authors in the extremal Reissner-Nordstrom black hole cases to non-extremal cases. Using the new analytical method, we revisit four-dimensional Reissner-Nordstrom black hole case and obtain that four-dimensional Reissner-Nordstrom black hole is superradiantly stable, which is consistent with results in previous works. We then analytically prove that the five-dimensional Reissner-Nordstrom black holes are also superradiantly stable under charged massive scalar perturbation. Our result implies that all higher dimensional non-extremal Reissner-Nordstrom black holes may be superradiantly stable under charged massive scalar perturbation.

Superradiant stability of five and six-dimensional extremal Reissner\u2013Nordstrom black holes

We revisit the superradiant stability of five and six-dimensional extremal Reissner–Nordstrom black holes under charged massive scalar perturbation with a new analytical method. In each case, it is analytically proved that the effective potential experienced by the scalar perturbation has only one maximum outside the black hole horizon and no potential well exists for the superradiance modes. So the five and six-dimensional extremal Reissner–Nordstrom black holes are superradiantly stable. The new method we developed is based on the Descartes’ rule of signs for the polynomial equations. Our result provides a complementary support of previous studies on the stability of higher dimensional extremal Reissner–Nordstrom black holes based on numerical methods.

Dyonic Reissner\u2013Nordstrom black holes and superradiant stability

Black holes immersed in magnetic fields are believed to be important systems in astrophysics. One interesting topic on these systems is their superradiant stability property. In the present paper, we analytically obtain the superradiantly stable regime for the asymptotically flat dyonic Reissner–Nordstrom black holes with charged massive scalar perturbation. The effective potential experienced by the scalar perturbation in the dyonic black hole background is obtained and analyzed. It is found that the dyonic black hole is superradiantly stable in the regime 0<r_{-}/r_{+}<2/3, where r_pm are the event horizons of the dyonic black hole. Compared with the purely electrically charged Reissner–Nordstrom black hole case, our result indicates that the additional coupling of the charged scalar perturbation with the magnetic filed makes the black hole and scalar perturbation system more superradiantly unstable, which provides further evidence on the instability induced by magnetic field in black hole superradiance process.

Extremal rotating black holes, scalar perturbation and superradiant stability

A (charged) rotating black hole may be unstable against a (charged) massive scalar field perturbation due to the existence of superradiance modes. The stability property depends on the parameters of the system. In this paper, the superradiant stable parameter space is studied for the four-dimensional extremal Kerr and Kerr-Newman black holes under massive and charged massive scalar perturbation. For the extremal Kerr case, it is found that when the angular frequency and proper mass of the scalar perturbation satisfy the inequality ω<μ/3, the extremal Kerr black hole and scalar perturbation system is superradiantly stable. For the Kerr-Newman black hole case, when the angular frequency of the scalar perturbation satisfies ω<qQ/M and the product of the mass-to-charge ratios of the black hole and scalar perturbation satisfies μqMQ>3k2+2k2+2,k=aM, the extremal Kerr-Newman black hole is superradiantly stable under charged massive scalar perturbation.

Analytic study of superradiant stability of Kerr\u2013Newman black holes under charged massive scalar perturbation

The superradiant stability of a Kerr–Newman black hole and charged massive scalar perturbation is investigated. We treat the black hole as a background geometry and study the equation of motion of the scalar perturbation. From the radial equation of motion, we derive the effective potential experienced by the scalar perturbation. By a careful analysis of this effective potential, it is found that when the inner and outer horizons of Kerr–Newman black hole satisfy frac{r_-}{r_+}leqslant frac{1}{3} and the charge-to-mass ratios of scalar perturbation and black hole satisfy frac{q}{mu }frac{Q}{ M}>1 , the Kerr–Newman black hole and scalar perturbation system is superradiantly stable.

Linear instability of charged massless scalar perturbation in regularized 4D charged Einstein-Gauss-Bonnet anti de-Sitter black holes * *Peng Liu is Supported by the Natural Science Foundation of China (11847055, 11905083). Chao Niu is Supported by the Natural Science Foundation of China (11805083). C. Y. Zhang is Supported by Natural Science Foundation of China (11947067, 12005077)

We study the linear instability of the charged massless scalar perturbation in regularized 4D charged Einstein-Gauss-Bonnet-AdS black holes by exploring their quasinormal modes. We find that the linear instability is triggered by superradiance. The charged massless scalar perturbation becomes more unstable with increasing Gauss-Bonnet coupling constant or black hole charge. Decreasing the AdS radius, on the other hand, will make the charged massless scalar perturbation more stable. The stable region in parameter space (α, Q, Λ) is given. Moreover, we find that the charged massless scalar perturbation is more unstable for larger scalar charge. The modes of multipoles are more stable than that of the monopole.

Instability of regularized 4D charged Einstein-Gauss-Bonnet de-Sitter black holes * *Supported by the National Natural Science Foundation of China (11847055, 11905083, 11805083, 11947067)

We studied the instability of regularized 4D charged Einstein-Gauss-Bonnet de-Sitter black holes under charged scalar perturbations. The unstable modes satisfy the superradiant condition, but not all of the modes satisfying the superradiant condition are unstable. The instability occurs when the cosmological constant is small and the black hole charge is not too large. The Gauss-Bonnet coupling constant further destabilizes black holes when both the black hole charge and the cosmological constant are small and further stabilizes black holes when the black hole charge is large.

Instability and no-hair paradigm in d-dimensional charged-AdS black holes

Is it possible the no-hair paradigm is violated when a black hole undergoes an instability? Employing massless charged scalar perturbations, we address this question within the context of conformally invariant Einstein-Maxwell theory for some allowed d-dimensional (d=4n+4 with conformal parameter n=0,1,2,...) topological small AdS black-holes. We provide numerical analyses that show the non trivial scalar hairy black hole solutions to include planar and spherical horizon topologies in higher dimensions with an even conformal parameter n. It is also shown that the solutions presented here cannot be considered as scalar hairs for a Reissner-Nordstrom background. As a result, for d-dimensional small AdS black holes in the presence of a conformally invariant Maxwell source, the no-scalar hair paradigm seems to be supported.

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.