31 research outputs found
Dilatonic BTZ black holes with power-law field
Motivated by low energy effective action of string theory and large
applications of BTZ black holes, we will consider minimal coupling between
dilaton and nonlinear electromagnetic fields in three dimensions. The main goal
is studying thermodynamical structure of black holes in this set up.
Temperature and heat capacity of these black holes are investigated and a
picture regarding their phase transitions is given. In addition, the role and
importance of studying the mass of black holes is highlighted. We will see how
different parameters modify thermodynamical quantities, hence thermodynamical
structure of these black holes. In addition, geometrical thermodynamics is used
to investigate thermodynamical properties of these black holes. In this regard,
the successful method is presented and the nature of interaction around bound
and phase transition points is studied.Comment: 15 pages, 8 figures, 1 table. accepted in Phys. Lett.
Effect of massive graviton on dark energy star structure
The presence of massive gravitons in the field of massive gravity is
considered as an important factor in investigating the structure of compact
objects. Hence, we are encouraged to study the dark energy star structure in
the Vegh's massive gravity. We consider that the equation of state governing
the inner spacetime of the star is the extended Chaplygin gas, and then using
this equation of state, we numerically solve the Tolman-Oppenheimer-Volkoff
(TOV) equation in massive gravity. In the following, assuming different values
of free parameters defined in massive gravity, we calculate the properties of
dark energy star such as radial pressure, transverse pressure, anisotropy
parameter, and other characteristics. Then, after obtaining the maximum mass
and its corresponding radius, we compute redshift and compactness. The obtained
results show that for this model of dark energy star, the maximum mass and its
corresponding radius depend on the massive gravity's free parameters and
anisotropy parameter. These results are consistent with the observational data,
and cover the lower mass gap. We also demonstrate that all energy conditions
are satisfied for this model, and in the presence of anisotropy, the dark
energy star is potentially unstable.Comment: 17 pages, 10 figures, 4 table
Effect of rainbow function on the structural properties of dark energy star
Confirming the existence of compact objects with a mass greater than
by observational results such as GW190814 makes that is possible
to provide theories to justify these observational results using modified
gravity. This motivates us to use gravity's rainbow, which is the appropriate
case for dense objects, to investigate the dark energy star structure as a
suggested alternative case to the mass gap between neutron stars and black
holes in the perspective of quantum gravity. Hence, in the present work, we
derive the modified hydrostatic equilibrium equation for an anisotropic fluid,
represented by the extended Chaplygin equation of state in gravity's rainbow.
Then, for two isotropic and anisotropic cases, using the numerical solution, we
obtain energy-dependent maximum mass and its corresponding radius, and the
other properties of the dark energy star including the pressure, energy
density, stability, etc. In the following, using the observational data, we
compare the obtained results in two frameworks of general relativity and
gravity's rainbow.Comment: 12 pages, 8 figures, 4 table
Some exact solutions of F(R) gravity with charged (a)dS black hole interpretation
In this paper we obtain topological static solutions of some kind of pure
gravity. The present solutions are two kind: first type is uncharged
solution which corresponds with the topological (a)dS Schwarzschild solution
and second type has electric charge and is equivalent to the
Einstein--conformally invariant Maxwell solution. In other word,
starting from pure gravity leads to (charged) Einstein- solutions
which we interpreted them as (charged) (a)dS black hole solutions of pure
gravity. Calculating the Ricci and Kreschmann scalars show that there is
a curvature singularity at . We should note that the Kreschmann scalar of
charged solutions goes to infinity as , but with a rate slower
than that of uncharged solutions.Comment: 21 pages, 4 figures, generalization to higher dimensions, references
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