Physics Letters B 773 (2017) 105–111
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Thermodynamics of novel charged dilatonic BTZ black holes
M. Dehghani
Department of Physics, Ilam University, Ilam, Iran
a r t i c l e i n f o a b s t r a c t
Article history:
Received
9 July 2017
Received
in revised form 31 July 2017
Accepted
2 August 2017
Available
online 10 August 2017
Editor:
N. Lambert
Keywords:
Charged
BTZ black hole
Charged
black hole with scalar hair
Maxwell’s
theory of electrodynamics
Three-dimensional
dilatonic black holes
In this paper, the three-dimensional Einstein–Maxwell theory in the presence of a dilatonic scalar field
has been studied. It has been shown that the dilatonic potential must be considered as the linear
combination of two Liouville-type potentials. Two new classes of charged dilatonic BTZ black holes, as
the exact solutions to the coupled scalar, vector and tensor field equations, have been obtained and
their properties have been studied. The conserved charge and mass of the new black holes have been
calculated, making use of the Gauss’s law and Abbott–Deser proposal, respectively. Through comparison
of the thermodynamical extensive quantities (i.e. temperature and entropy) obtained from both, the
geometrical and the thermodynamical methods, the validity of the first law of black hole thermodynamics
has been confirmed for both of the new black holes we just obtained. A black hole thermal stability or
phase transition analysis has been performed, making use of the canonical ensemble method. Regarding
the black hole heat capacity, it has been found that for either of the new black hole solutions there are
some specific ranges in such a way that the black holes with the horizon radius in these ranges are
locally stable. The points of type one and type two phase transitions have been determined. The black
holes, with the horizon radius equal to the transition points are unstable. They undergo type one or type
two phase transitions to be stabilized.
© 2017 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP
3
.
1. Introduction
Although the Einstein’s tensorial theory of gravitation is in
agreement with a large amount of observational tests, but it fails
regarding some important issues [1–5]. Modification of the Ein-
stein’s
theory of gravity is one of the main approaches to over-
come
the related failures. Among the various proposed modifi-
cations
[6–13], the so-called scalar-tensor theories [14], as the
modification arisen from string theory, have provided interesting
results [15]. The Einstein’s action is naturally modified by the
scalar-tensor superstring terms at the high energy regime. In the
low energy limit of the string theory, the Einstein’s theory of grav-
ity
is recovered which is coupled to a dilatonic scalar field [16].
Black
holes with scalar hair are interesting solutions of Ein-
stein’s
theory of gravity and also of certain types of modified
gravity theories. These solutions have been investigated by theo-
retical
physicists in four and higher dimensional space times for
a long time (see [17] and references therein). The first studies on
the three-dimensional black holes, as the interesting predictions
of Einstein’s theory of relativity in lower dimensional space times,
have been done by Banados, Teitelboim, and Zanelli (BTZ) [18].
E-mail address: m.dehghani@ilam.ac.ir.
Investigation of the three-dimensional black holes is one of the in-
teresting
subjects for recent gravitational studies [19]. Chan and
Mann [20], are the first authors who investigated the charged
three-dimensional dilatonic black holes in the presence of a mini-
mally
coupled logarithmic dilaton field.
It
is a commonly believed that study of three-dimensional so-
lutions
help us to find a deeper insight into the fundamental ideas
in comparison to higher dimensional black holes. Also, according to
(A)dS/CFT correspondence, there is a dual between quantum grav-
ity
on A(dS) space and Euclidean conformal field theory on the
lower dimensional space times [21,22]. From this point of view,
study of physics in (2 +1)-dimensional space times can be useful
for understanding of quantum field theory on A(dS) spacetimes.
Although this subject area has been considered extensively [23], it
still has many unknown and interesting parts to be studied [24].
On
the other hand, after the discoveries of Bekenstein, Bardeen,
Carter and Hawking, it is well-known that black holes can be
considered as the thermodynamical systems with a temperature
proportional to the surface gravity and having pure geometrical
entropy equal to one-fourth of the horizon area [25–27]. When a
dilatonic scalar field is coupled to the three-dimensional Einstein–
Maxwell
theory, it is expected to produce new and interesting
consequences for the black hole solutions. Thus, it is worth to find
exact solutions of Einstein–Maxwell theory in the presence of a
http://dx.doi.org/10.1016/j.physletb.2017.08.003
0370-2693/
© 2017 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by
SCOAP
3
.