11,361 research outputs found
Horizon thermodynamics in fourth-order gravity
In the framework of horizon thermodynamics, the field equations of Einstein
gravity and some other second-order gravities can be rewritten as the
thermodynamic identity: . However, in order to construct the
horizon thermodynamics in higher-order gravity, we have to simplify the field
equations firstly. In this paper, we study the fourth-order gravity and convert
it to second-order gravity via a so-called " Legendre transformation " at the
cost of introducing two other fields besides the metric field. With this
simplified theory, we implement the conventional procedure in the construction
of the horizon thermodynamics in 3 and 4 dimensional spacetime. We find that
the field equations in the fourth-order gravity can also be written as the
thermodynamic identity. Moreover, we can use this approach to derive the same
black hole mass as that by other methods.Comment: 12 pages, no figur
-dimensional regular black holes with nonlinear electrodynamics sources
On the basis of two requirements: the avoidance of the curvature singularity
and the Maxwell theory as the weak field limit of the nonlinear
electrodynamics, we find two restricted conditions on the metric function of
-dimensional regular black hole in general relativity coupled with
nonlinear electrodynamics sources. By the use of the two conditions, we obtain
a general approach to construct -dimensional regular black holes. In
this manner, we construct four -dimensional regular black holes as
examples. We also study the thermodynamic properties of the regular black holes
and verify the first law of black hole thermodynamics.Comment: 13 pages, 4 figures. in press in PL
Stability of black holes based on horizon thermodynamics
On the basis of horizon thermodynamics we study the thermodynamic stability
of black holes constructed in general relativity and Gauss-Bonnet gravity. In
the framework of horizon thermodynamics there are only five thermodynamic
variables . It is not necessary to consider concrete matter fields,
which may contribute to the pressure of black hole thermodynamic system. In
non-vacuum cases, we can derive the equation of state, . According to
the requirements of stable equilibrium in conventional thermodynamics, we start
from these thermodynamic variables to calculate the heat capacity at constant
pressure and Gibbs free energy and analyze the local and global thermodynamic
stability of black holes. It is shown that is the necessary condition for
black holes in general relativity to be thermodynamically stable, however this
condition cannot be satisfied by many black holes in general relativity. For
black hole in Gauss-Bonnet gravity negative pressure can be feasible, but only
local stable black hole exists in this case.Comment: 6 pages, 7 figure
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