14 research outputs found
Particle collisions near a three-dimensional warped AdS black hole
In this paper we consider the warped AdS black hole solution of
topologically massive gravity with a negative cosmological constant, and we
investigate the possibility that it acts as a particle accelerator by analyzing
the energy in the center of mass (CM) frame of two colliding particles in the
vicinity of its horizon, which is known as the Ba\~nados, Silk and West (BSW)
process. Mainly, we show that the critical angular momentum of the
particle decreases when the parameter that controls the stretching deformation
() increases. Also, we show that despite the particle with can exist
for certain values of the conserved energy outside the horizon, it will never
reach the event horizon; therefore, the black hole can not act as a particle
accelerator with arbitrarily high CM energy on the event horizon. However, such
particle could also exist inside the outer horizon being the BSW process
possible on the inner horizon. On the other hand, for the extremal warped
AdS black hole, the particle with and energy could exist
outside the event horizon and the CM energy blows up on the event horizon if
its conserved energy fulfill the condition
, being the BSW process possible.Comment: 11 pages, 6 figure
Charged scalar field perturbations in Ernst black holes
We consider the propagation of a charged massive scalar field in the
background of a four-dimensional Ernst black hole and study its stability
analyzing the quasinormal modes (QNMs), which are calculated using the
semi-analytical Wentzel-Kramers-Brillouin method and numerically using the
continued fraction method. Mainly, we find that for a scalar field mass less
than a critical mass, the decay rate of the QNMs decreases when the harmonic
angular number increases; and for a scalar field mass greater than the
critical mass the behaviour is inverted, i.e, the longest-lived modes are
always the ones with the lowest angular number recovering the standard
behaviour. Also, we find a critical value of the external magnetic field, as
well as, a critical value of the scalar field charge that exhibit the same
behaviour with respect to the angular harmonic numbers. In addition, we show
that the spacetime allows stable quasibound states and we observe a splitting
of the spectrum due to the Zeeman effect. Finally, we show that the unstable
null geodesic in the equatorial plane is connected with the QNMs when the
azimuthal quantum number satisfy in the eikonal limit.Comment: 14 pages and 7 figures. arXiv admin note: text overlap with
arXiv:gr-qc/0211035 by other author
Quasinormal modes of a charged scalar field in Ernst black holes
We consider the propagation of a charged massive scalar field in the background of a four-dimensional Ernst black hole and study its stability analyzing the quasinormal modes (QNMs), which are calculated using the semi-analytical Wentzel–Kramers–Brillouin method and numerically using the continued fraction method. We mainly find that for a scalar field mass less than a critical mass, the decay rate of the QNMs decreases when the harmonic angular number increases; and for a scalar field mass greater than the critical mass, the behavior is inverted, i.e., the longest-lived modes are always the ones with the lowest angular number recovering the standard behavior. Also, we find a critical value of the external magnetic field, as well as a critical value of the scalar field charge that exhibits the same behavior with respect to the angular harmonic numbers. In addition, we show that the spacetime allows stable quasibound states, and we observe a splitting of the spectrum due to the Zeeman effect. Finally, we show that the unstable null geodesic in the equatorial plane is connected with the QNMs when the azimuthal quantum number satisfies in the eikonal limit
Collision of particles near a three-dimensional rotating Hořava AdS black hole
We consider a three-dimensional rotating AdS black hole, which is a solution of Hořava gravity in the low-energy limit that corresponds to a Lorentz-violating version of the BTZ black hole, and we analyze the effect of the breaking of Lorentz invariance on the possibility that the black hole can act as a particle accelerator by analyzing the energy in the center-of-mass (CM) frame of two colliding particles in the vicinity of its horizons. We find that the critical angular momentum of particles increases when the Hořava parameter increases and when the aether parameter b increases. Also, the particles can collide on the inner horizon with arbitrarily high CM energy if one of the particles has a critical angular momentum, possible for the BSW process. Here it is essential that, while for the extremal BTZ black hole the particles with critical angular momentum only can exist on the degenerate horizon, for the Lorentz-violating version of the BTZ black hole the particle with critical angular momentum can exist in a region away from the degenerate horizon. It is worth mentioning that the results exposed in this manuscript can be applied for the covariant version of Hořava gravity, where the covariant definition of the center-of-mass energy is well defined
Perturbative and nonperturbative quasinormal modes of 4D Einstein–Gauss–Bonnet black holes
We study the propagation of probe scalar fields in the background of 4D Einstein–Gauss–Bonnet black holes with anti-de Sitter (AdS) asymptotics and calculate the quasinormal modes. Mainly, we show that the quasinormal spectrum consists of two different branches, a branch perturbative in the Gauss–Bonnet coupling constant and another branch, nonperturbative in . The perturbative branch consists of complex quasinormal frequencies that approximate the quasinormal frequencies of the Schwarzschild AdS black hole in the limit of a null coupling constant. On the other hand, the nonperturbative branch consists of purely imaginary frequencies and is characterized by the growth of the imaginary part when decreases, diverging in the limit of null coupling constant; therefore they do not exist for the Schwarzschild AdS black hole. Also, we find that the imaginary part of the quasinormal frequencies is always negative for both branches; therefore, the propagation of scalar fields is stable in this background