93 research outputs found
Minimal Log Gravity
Minimal Massive Gravity (MMG) is an extension of three-dimensional
Topologically Massive Gravity that, when formulated about Anti-de Sitter space,
accomplishes to solve the tension between bulk and boundary unitarity that
other models in three dimensions suffer from. We study this theory at the
chiral point, i.e. at the point of the parameter space where one of the central
charges of the dual conformal field theory vanishes. We investigate the
non-linear regime of the theory, meaning that we study exact solutions to the
MMG field equations that are not Einstein manifolds. We exhibit a large class
of solutions of this type, which behave asymptotically in different manners. In
particular, we find analytic solutions that represent two-parameter
deformations of extremal Banados-Teitelboim-Zanelli (BTZ) black holes. These
geometries behave asymptotically as solutions of the so-called Log Gravity,
and, despite the weakened falling-off close to the boundary, they have finite
mass and finite angular momentum, which we compute. We also find time-dependent
deformations of BTZ that obey Brown-Henneaux asymptotic boundary conditions.
The existence of such solutions show that Birkhoff theorem does not hold in MMG
at the chiral point. Other peculiar features of the theory at the chiral point,
such as the degeneracy it exhibits in the decoupling limit of the Cotton
tensor, are discussed.Comment: 13 pages. v2 minor typos corrected. Accepted for publication in Phys.
Rev.
AdS and Lifshitz black hole solutions in conformal gravity sourced with a scalar field
In this paper we obtain exact asymptotically anti-de Sitter black hole
solutions and asymptotically Lifshitz black hole solutions with dynamical
exponents and of four-dimensional conformal gravity coupled with a
self-interacting conformally invariant scalar field. Then, we compute their
thermodynamical quantities, such as the mass, the Wald entropy and the Hawking
temperature. The mass expression is obtained by using the generalized off-shell
Noether potential formulation. It is found that the anti-de Sitter black holes
as well as the Lifshitz black holes with have zero mass and zero entropy,
although they have non-zero temperature. A similar behavior has been observed
in previous works, where the integration constant is not associated with a
conserved charge, and it can be interpreted as a kind of gravitational hair. On
the other hand, the Lifshitz black holes with dynamical exponent have
non-zero conserved charges, and the first law of black hole thermodynamics
holds. Also, we analyze the horizon thermodynamics for the Lifshitz black holes
with , and we show that the first law of black hole thermodynamics arises
from the field equations evaluated on the horizon. Furthermore, we study the
propagation of a conformally coupled scalar field on these backgrounds and we
find the quasinormal modes analytically in several cases. We find that for
anti-de Sitter black holes and Lifshitz black holes with , there is a
continuous spectrum of frequencies for Dirichlet boundary condition; however,
we show that discrete sets of well defined quasinormal frequencies can be
obtained by considering Neumann boundary conditions
About the coordinate time for photons in Lifshitz Space-times
In this paper we studied the behavior of radial photons from the point of
view of the coordinate time in (asymptotically) Lifshitz space-times, and we
found a generalization to the result reported in previous works by Cruz et. al.
[Eur. Phys. J. C {\bf 73}, 7 (2013)], Olivares et. al. [Astrophys. Space Sci.
{\bf 347}, 83-89 (2013)], and Olivares et. al. [arXiv: 1306.5285]. We
demonstrate that all asymptotically Lifshitz space-times characterized by a
lapse funcion which tends to one when , present the
same behavior, in the sense that an external observer will see that photons
arrive at spatial infinity in a finite coordinate time. Also, we show that
radial photons in the proper system cannot determine the presence of the black
hole in the region , because the proper time results to be
independent of the lapse function .Comment: 5 pages, 4 figures, accepted for publication on EPJ
Fermionic greybody factors of two and five-dimensional dilatonic black holes
We study fermionic perturbations in the background of a two and
five-dimensional dilatonic black holes. Then, we compute the reflection and
transmission coefficients and the absorption cross section for fermionic
fields, and we show numerically that the absorption cross section vanishes in
the low and high frequency limit. Also we find that beyond a certain value of
the horizon radius the absorption cross section for five-dimensional
dilatonic black hole is constant. Besides, we have find that the absorption
cross section decreases for higher angular momentum, and it decreases when the
mass of the fermionic field increases.Comment: Accepted in EPJ
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
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