487 research outputs found
Thermodynamics of a black hole in a cavity
We present a unified thermodynamical description of the configurations
consisting on self-gravitating radiation with or without a black hole. We
compute the thermal fluctuations and evaluate where will they induce a
transition from metastable configurations towards stable ones. We show that the
probability of finding such a transition is exponentially small. This indicates
that, in a sequence of quasi equilibrium configurations, the system will remain
in the metastable states till it approaches very closely the critical point
beyond which no metastable configuration exists. Near that point, we relate the
divergence of the local temperature fluctuations to the approach of the
instability of the whole system, thereby generalizing the usual fluctuations
analysis in the cases where long range forces are present. When angular
momentum is added to the cavity, the above picture is slightly modified.
Nevertheless, at high angular momentum, the black hole loses most of its mass
before it reaches the critical point at which it evaporates completely.Comment: 27 pages, latex file, contains 3 figures available on request at
[email protected]
Discrete-time classical and quantum Markovian evolutions: Maximum entropy problems on path space
The theory of Schroedinger bridges for diffusion processes is extended to
classical and quantum discrete-time Markovian evolutions. The solution of the
path space maximum entropy problems is obtained from the a priori model in both
cases via a suitable multiplicative functional transformation. In the quantum
case, nonequilibrium time reversal of quantum channels is discussed and
space-time harmonic processes are introduced.Comment: 34 page
Causal Relativistic Fluid Dynamics
We derive causal relativistic fluid dynamical equations from the relaxation
model of kinetic theory as in a procedure previously applied in the case of
non-relativistic rarefied gases. By treating space and time on an equal footing
and avoiding the iterative steps of the conventional Chapman-Enskog ---
CE---method, we are able to derive causal equations in the first order of the
expansion in terms of the mean flight time of the particles. This is in
contrast to what is found using the CE approach. We illustrate the general
results with the example of a gas of identical ultrarelativistic particles such
as photons under the assumptions of homogeneity and isotropy. When we couple
the fluid dynamical equations to Einstein's equation we find, in addition to
the geometry-driven expanding solution of the FRW model, a second,
matter-driven nonequilibrium solution to the equations. In only the second
solution, entropy is produced at a significant rate.Comment: 23 pages (CQG, in press
Attenuation and damping of electromagnetic fields: Influence of inertia and displacement current
New results for attenuation and damping of electromagnetic fields in rigid
conducting media are derived under the conjugate influence of inertia due to
charge carriers and displacement current. Inertial effects are described by a
relaxation time for the current density in the realm of an extended Ohm's law.
The classical notions of poor and good conductors are rediscussed on the basis
of an effective electric conductivity, depending on both wave frequency and
relaxation time. It is found that the attenuation for good conductors at high
frequencies depends solely on the relaxation time. This means that the
penetration depth saturates to a minimum value at sufficiently high
frequencies. It is also shown that the actions of inertia and displacement
current on damping of magnetic fields are opposite to each other. That could
explain why the classical decay time of magnetic fields scales approximately as
the diffusion time. At very small length scales, the decay time could be given
either by the relaxation time or by a fraction of the diffusion time, depending
whether inertia or displacement current, respectively, would prevail on
magnetic diffusion.Comment: 21 pages, 1 figur
Cosmological entropy and generalized second law of thermodynamics in theory of gravity
We consider a spatially flat Friedmann-Lemaitre-Robertson-Walker space time
and investigate the second law and the generalized second law of thermodynamics
for apparent horizon in generalized modified Gauss Bonnet theory of gravity
(whose action contains a general function of Gauss Bonnet invariant and the
Ricci scalar: ). By assuming that the apparent horizon is in thermal
equilibrium with the matter inside it, conditions which must be satisfied by
are derived and elucidated through two examples: a quasi-de Sitter
space-time and a universe with power law expansion.Comment: 10 pages, minor changes, typos corrected, accepted for publication in
Europhysics Letter
Lemaitre-Tolman-Bondi dust spacetimes: Symmetry properties and some extensions to the dissipative case
We consider extensions of Lemaitre-Tolman-Bondi (LTB) spacetimes to the
dissipative case. For doing that we previously carry out a systematic study on
LTB. This study is based on two different aspects of LTB. On the one hand, a
symmetry property of LTB will be presented. On the other hand, the description
of LTB in terms of some fundamental scalar functions (structure scalars)
appearing in the orthogonal splitting of Riemann tensor will be provided. We
shall consider as "natural" generalizations of LTB (hereafter referred to as
GLTB) either those metrics admitting some similar kind of symmetry as LTB, or
those sharing structure scalars with similar dependence on the metric.Comment: 13 pages RevTex. To appear in Phys. Rev. D. Some references corrected
and update
Holographic Dark Energy with Curvature
In this paper we consider an holographic model of dark energy, where the
length scale is the Hubble radius, in a non flat geometry. The model contains
the possibility to alleviate the cosmic coincidence problem, and also
incorporate a mechanism to obtain the transition from decelerated to an
accelerated expansion regime. We derive an analytic form for the Hubble
parameter in a non flat universe, and using it, we perform a Bayesian analysis
of this model using SNIa, BAO and CMB data. We find from this analysis that the
data favored a small value for , however high enough to still produce
cosmological consequences.Comment: 6 pages, 2 figure
Thermodynamics of black holes: an analogy with glasses
The present equilibrium formulation of thermodynamics for black holes has
several drawbacks, such as assuming the same temperature for black hole and
heat bath. Recently the author formulated non-equilibrium thermodynamics for
glassy systems. This approach is applied to black holes, with the cosmic
background temperature being the bath temperature, and the Hawking temperature
the internal temperature. Both Hawking evaporation and absorption of background
radiation are taken into account.
It is argued that black holes did not form in the very early universe.Comment: 4 pages revtex; submitted to Phys. Rev. Let
The imprint of the interaction between dark sectors in galaxy clusters
Based on perturbation theory, we study the dynamics of how dark matter and
dark energy in the collapsing system approach dynamical equilibrium while
interacting. We find that the interaction between dark sectors cannot ensure
the dark energy to fully cluster along with dark, leading to the energy
non-conservation problem in the collapsing system We examine the cluster number
counts dependence on the interaction between dark sectors. Furthermore, we
analyze how dark energy inhomogeneities affect cluster abundances. It is shown
that cluster number counts can provide specific signature of dark sectors
interaction and dark energy inhomogeneities.Comment: revised version. New treatment has been provided on studying the
structure formation in the spherical collapsing system where DE does not
cluster together with DM. Accepted for publication in JCA
The imprint of the interaction between dark sectors in galaxy clusters
Based on perturbation theory, we study the dynamics of how dark matter and
dark energy in the collapsing system approach dynamical equilibrium while
interacting. We find that the interaction between dark sectors cannot ensure
the dark energy to fully cluster along with dark, leading to the energy
non-conservation problem in the collapsing system We examine the cluster number
counts dependence on the interaction between dark sectors. Furthermore, we
analyze how dark energy inhomogeneities affect cluster abundances. It is shown
that cluster number counts can provide specific signature of dark sectors
interaction and dark energy inhomogeneities.Comment: revised version. New treatment has been provided on studying the
structure formation in the spherical collapsing system where DE does not
cluster together with DM. Accepted for publication in JCA
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