3,847 research outputs found
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
Noncommutative geometry inspired black holes in Rastall gravity
Under two different metric ansatzes, the noncommutative geometry inspired
black holes (NCBH) in the framework of Rastall gravity are derived and
analyzed. We consider the fluid-type matter with the Gaussian-distribution
smeared mass density. Taking a Schwarzschild-like metric ansatz, it is shown
that the noncommutative geometry inspired Schwarzschild black hole (NCSBH) in
Rastall gravity, unlike its counterpart in general relativity (GR), is not a
regular black hole. It has at most one event horizon. After showing a finite
maximal temperature, the black hole will leave behind a point-like massive
remnant at zero temperature. Considering a more general metric ansatz and a
special equation of state of the matter, we also find a regular NCBH in Rastall
gravity, which has a similar geometric structure and temperature to that of
NCSBH in GR.Comment: 12 pages, 5 figures. to match the published versio
Tachyon field inspired dark energy and supernovae constraints
The tachyon field in cosmology is studied by applying the generating function
method to obtain exact solutions. The equation of state parameter of the
tachyon field is , which can be expressed as a
function in terms of the redshift . Based on these solutions, we propose
some tachyon-inspired dark energy models to explore the properties of the
corresponding cosmological evolution. The explicit relations between Hubble
parameter and redshift enable us to test the models with SNe Ia data sets
easily. In the current work we employ the SNe Ia data with the parameter
measured from the SDSS and the shift parameter from
WMAP observations to constrain the parameters in our models.Comment: 6 pages, 2 figures; v2: accepted by IJMP
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