Quasinormal modes and their anomalous behavior for black holes in f ( R ) gravity
TL;DR: In this paper, the authors analyzed the anomalous decay rate of the quasinormal modes (QNMs) of a massive scalar field in the background of an asymptotically de Sitter black hole solution in f(R) gravity.
Abstract: We study the propagation of scalar fields in the background of an asymptotically de Sitter black hole solution in f(R) gravity. The aim of this work is to analyze in modified theories of gravity the existence of an anomalous decay rate of the quasinormal modes (QNMs) of a massive scalar field which was recently reported in Schwarzschild black hole backgrounds, in which the longest-lived modes are the ones with higher angular number, for a scalar field mass smaller than a critical value, while that beyond this value the behavior is inverted. We study the QNMs for various overtone numbers and they depend on a parameter $$\beta $$
which appears in the metric and characterizes the f(R) gravity. For small $$\beta $$
, i.e. small deviations from the Schwarzschild–dS black hole the anomalous behavior in the QNMs is present for the photon sphere modes, and the critical value of the mass of the scalar field depends on the parameter $$\beta $$
while for large $$\beta $$
, i.e. large deviations, the anomalous behavior and the critical mass does not appear. Also, the critical mass of the scalar field increases when the overtone number increases until the f(R) gravity parameter $$\beta $$
approaches the near extremal limit at which the critical mass of the scalar field does not depend anymore on the overtone number. The imaginary part of the quasinormal frequencies is always negative leading to a stable propagation of the scalar fields in this background.
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TL;DR: In this paper, the authors considered f(R) gravity theories in the presence of a scalar field minimally coupled to gravity with a self-interacting potential and found scalarized black hole solutions at small distances.
Abstract: We consider f(R) gravity theories in the presence of a scalar field minimally coupled to gravity with a self-interacting potential. When the scalar field backreacts to the metric we find at large distances scalarized Schwarzschild-AdS and Schwarzschild-AdS-like black hole solutions. At small distances due to strong curvature effects and the scalar dynamis we find a rich structure of scalarized black hole solutions. When the scalar field is conformally coupled to gravity we also find scalarized black hole solutions at small distances.
27 citations
TL;DR: In this article , the quasinormal modes (QNM) frequencies of a test massless scalar field and an electromagnetic field around static black holes in f(T) gravity were derived.
Abstract: We calculate the quasinormal modes (QNM) frequencies of a test massless scalar field and an electromagnetic field around static black holes in f(T) gravity. Focusing on quadratic f(T) modifications, which is a good approximation for every realistic f(T) theory, we first extract the spherically symmetric solutions using the perturbative method, imposing two ansätze for the metric functions, which suitably quantify the deviation from the Schwarzschild solution. Moreover, we extract the effective potential, and then calculate the QNM frequency of the obtained solutions. Firstly, we numerically solve the Schrödinger-like equation using the discretization method, and we extract the frequency and the time evolution of the dominant mode applying the function fit method. Secondly, we perform a semi-analytical calculation by applying the WKB method with the Pade approximation. We show that the results for f(T) gravity are different compared to General Relativity, and in particular we obtain a different slope and period of the field decay behavior for different model parameter values. Hence, under the light of gravitational-wave observations of increasing accuracy from binary systems, the whole analysis could be used as an additional tool to test General Relativity and examine whether torsional gravitational modifications are possible.
12 citations
TL;DR: In this article, the authors studied the propagation of charged scalar fields in the background of $2+1$-dimensional Coulomb-like AdS black holes, and showed that such propagation is unstable under Dirichlet boundary conditions.
Abstract: We study the propagation of charged scalar fields in the background of $2+1$-dimensional Coulomb-like AdS black holes, and we show that such propagation is unstable under Dirichlet boundary conditions. However, all the unstable modes are superradiant and all the stable modes are nonsuperradiant, according with the superradiant condition. Mainly, we show that when the scalar field is charged the quasinormal frecuencies (QNFs) are always complex, contrary to the uncharged case, where for small values of the black hole charge the complex QNFs are dominant, while that for bigger values of the black hole charge the purely imaginary QNFs are dominant.
11 citations
TL;DR: In this paper , a self-interacting scalar field nonminimally coupled to gravity is considered and the Ricci scalar receives a nonlinear correction term which breaks the conformal invariance and leads to a massless black hole solution.
Abstract: We consider a $f(R)$ gravity theory in ($2+1$)-dimensions with a self-interacting scalar field nonminimally coupled to gravity. Without specifying the form of the $f(R)$ function, solving the field equations we find that the Ricci scalar receives a nonlinear correction term which breaks the conformal invariance and leads to a massless black hole solution. When the nonlinear term decouples, we get a well-known hairy black hole solution with the scalar field conformally coupled to gravity. We also find that the entropy of our black hole may be higher than the corresponding conformal black hole which indicates that our solution may be thermodynamically preferred.
10 citations
TL;DR: In this article , a Generalized Bronnikov-Ellis wormhole and the tideless Morris-Thorne wormhole were considered and the propagation of massive scalar fields was studied.
Abstract: In this work we consider a Generalized Bronnikov-Ellis wormhole and the tideless Morris-Thorne wormhole and we study the propagation of massive scalar fields. We calculate the quasinormal frequencies using the WKB method and the pseudospectal Chebyshev method and we show the presence of an anomalous decay rate for the quasinormal modes in the Generalized Bronnikov-Ellis wormhole. However, such anomalous behaviour is avoided for the fundamental mode in the Morris-Thorne wormhole background.
5 citations
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