91 research outputs found
Quantum entropy of two-dimensional extreme charged dilaton black hole
By using Hawking's treatment as well as Zaslavskii's treatment respectively
and the brick wall model, two different values of classical entropy and quantum
entropy of scalar fields in the two-dimensional extreme charged dilaton black
hole backgrounds have been obtained. A new divergent term emerges in the
quantum entropy under the extreme limit for Zaslavskii's treatment and its
connection with the phase transition has been addressed.Comment: Latex version, to be published on Phys.Lett.
Effective spatial dimension of extremal non-dilatonic black p-branes and the description of entropy on the world volume
By investigating the critical behavior appearing at the extremal limit of the
non-dilatonic, black p-branes in (d+p) dimensions, we find that some critical
exponents related to the critical point obey the scaling laws. From the scaling
laws we obtain that the effective spatial dimension of the non-dilatonic black
holes and black strings is one, and is p for the non-dilatonic black p-branes.
For the dilatonic black holes and black p-branes, the effective dimension will
depend on the parameters in theories. Thus, we give an interpretation why the
Bekenstein-Hawking entropy may be given a simple world volume interpretation
only for the non-dilatonic black p-branes.Comment: 4 pages, RevTex, no figures, to appear in Phys. Rev. Let
Self-Similar Solutions for Viscous and Resistive ADAF
In this paper, the self-similar solution of resistive advection dominated
accretion flows (ADAF) in the presence of a pure azimuthal magnetic field is
investigated. The mechanism of energy dissipation is assumed to be the
viscosity and the magnetic diffusivity due to turbulence in the accretion flow.
It is assumed that the magnetic diffusivity and the kinematic viscosity are not
constant and vary by position and -prescription is used for them. In
order to solve the integrated equations that govern the behavior of the
accretion flow, a self-similar method is used. The solutions show that the
structure of accretion flow depends on the magnetic field and the magnetic
diffusivity. As, the radial infall velocity and the temperature of the flow
increase, and the rotational velocity decreases. Also, the rotational velocity
for all selected values of magnetic diffusivity and magnetic field is
sub-Keplerian. The solutions show that there is a certain amount of magnetic
field that the rotational velocity of the flow becomes zero. This amount of the
magnetic field depends on the gas properties of the disc, such as adiabatic
index and viscosity, magnetic diffusivity, and advection parameters. The
solutions show the mass accretion rate increases by adding the magnetic
diffusivity and in high magnetic pressure case, the ratio of the mass accretion
rate to the Bondi accretion rate decreases as magnetic field increases. Also,
the study of Lundquist and magnetic Reynolds numbers based on resistivity
indicates that the linear growth of magnetorotational instability (MRI) of the
flow decreases by resistivity. This property is qualitatively consistent with
resistive magnetohydrodynamics (MHD) simulations.Comment: 18 pages, 3 figures, accepted by JA&
Stability of Non-Abelian Black Holes
Two types of self-gravitating particle solutions found in several theories
with non-Abelian fields are smoothly connected by a family of non-trivial black
holes. There exists a maximum point of the black hole entropy, where the
stability of solutions changes. This criterion is universal, and the changes in
stability follow from a catastrophe-theoretic analysis of the potential
function defined by black hole entropy.Comment: 4 Figures to be sent on request,8 pages, WU-AP/33/9
Radionic Non-uniform Black Strings
Non-uniform black strings in the two-brane system are investigated using the
effective action approach. It is shown that the radion acts as a non-trivial
hair of the black strings. From the brane point of view, the black string
appears as the deformed dilatonic black hole which becomes dilatonic black hole
in the single brane limit and reduces to the Reissner-Nordstr\"om black hole in
the close limit of two-branes. The stability of solutions is demonstrated using
the catastrophe theory. From the bulk point of view, the black strings are
proved to be non-uniform. Nevertheless, the zeroth law of black hole
thermodynamics still holds.Comment: 9 pages, 6 figure
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