12,725 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
Exact solutions of embedding the four-dimensional perfect fluid in a five- or higher-dimensional Einstein spacetime and the cosmological interpretations
We investigate an exact solution that describes the embedding of the
four-dimensional (4D) perfect fluid in a five-dimensional (5D) Einstein
spacetime. The effective metric of the 4D perfect fluid as a hypersurface with
induced matter is equivalent to the Robertson-Walker metric of cosmology. This
general solution shows interconnections among many 5D solutions, such as the
solution in the braneworld scenario and the topological black hole with
cosmological constant. If the 5D cosmological constant is positive, the metric
periodically depends on the extra dimension. Thus we can compactify the extra
dimension on and study the phenomenological issues. We also generalize
the metric ansatz to the higher-dimensional case, in which the 4D part of the
Einstein equations can be reduced to a linear equation.Comment: 8 pages, 1 figures; v2: minor errors corrected; v3: references added;
v4: matches the version to appear in PL
Octet-baryon masses in finite space
We report on a recent study of finite-volume effects on the lowest-lying
octet baryon masses using the covariant baryon chiral perturbation theory up to
next-to-leading order by analysing the latest lattice QCD results
from the NPLQCD Collaboration.Comment: 4 pages, 1 figure; parallel talk delivered by XLR at the 14th
national conference on nuclear structure, April 12nd - 16th, 2012, Huzhou,
Chin
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