597 research outputs found
Galilean Limit of Equilibrium Relativistic Mass Distribution
The low-temperature form of the equilibrium relativistic mass distribution is
subject to the Galilean limit by taking In this limit
the relativistic Maxwell-Boltzmann distribution passes to the usual
nonrelativistic form and the Dulong-Petit law is recovered.Comment: TAUP-2081-9
Potential flows in a core-dipole-shell system: numerical results
Numerical solutions for: the integral curves of the velocity field
(streamlines), the density contours, and the accretion rate of a steady-state
flow of an ideal fluid with p=K n^(gamma) equation of state orbiting in a
core-dipole-shell system are presented. For 1 < gamma < 2, we found that the
non-linear contribution appearing in the partial differential equation for the
velocity potential has little effect in the form of the streamlines and density
contour lines, but can be noticed in the density values. The study of several
cases indicates that this appears to be the general situation. The accretion
rate was found to increase when the constant gamma decreases.Comment: RevTex, 8 pages, 5 eps figures, CQG to appea
Quantum vacuum effects as generalized f(R) gravity. Application to stars
It is assumed that, for weak spacetime curvature, the main gravitational
effect of the quantum vacuum stress-energy corresponds to adding two terms to
the Einstein-Hilbert action, proportional to the square of the curvature scalar
and to the contraction of two Ricci tensors, respectively. It is shown that
compatibility with terrestrial and solar systems observaction implies that the
square roorts of the coefficients of these terms should be either a few
millimeters or a few hundred meters. It is shown that the vacuum contribution
increase the stability of white dwarfs.Comment: GEneralizes and improves previous versio
The Problem of Inertia in Friedmann Universes
In this paper we study the origin of inertia in a curved spacetime,
particularly the spatially flat, open and closed Friedmann universes. This is
done using Sciama's law of inertial induction, which is based on Mach's
principle, and expresses the analogy between the retarded far fields of
electrodynamics and those of gravitation. After obtaining covariant expressions
for electromagnetic fields due to an accelerating point charge in Friedmann
models, we adopt Sciama's law to obtain the inertial force on an accelerating
mass by integrating over the contributions from all the matter in the
universe. The resulting inertial force has the form , where
depends on the choice of the cosmological parameters such as ,
, and and is also red-shift dependent.Comment: 10 page
Linear waves in sheared flows. Lower bound of the vorticity growth and propagation discontinuities in the parameters space
This study provides sufficient conditions for the temporal monotonic decay of
enstrophy for two-dimensional perturbations traveling in the incompressible,
viscous, plane Poiseuille and Couette flows. Extension of J. L. Synge's
procedure (1938) to the initial-value problem allowed us to find the region of
the wavenumber-Reynolds number map where the enstrophy of any initial
disturbance cannot grow. This region is wider than the kinetic energy's one. We
also show that the parameters space is split in two regions with clearly
distinct propagation and dispersion properties
All order covariant tubular expansion
We consider tubular neighborhood of an arbitrary submanifold embedded in a
(pseudo-)Riemannian manifold. This can be described by Fermi normal coordinates
(FNC) satisfying certain conditions as described by Florides and Synge in
\cite{FS}. By generalizing the work of Muller {\it et al} in \cite{muller} on
Riemann normal coordinate expansion, we derive all order FNC expansion of
vielbein in this neighborhood with closed form expressions for the curvature
expansion coefficients. Our result is shown to be consistent with certain
integral theorem for the metric proved in \cite{FS}.Comment: 27 pages. Corrected an error in a class of coefficients resulting
from a typo. Integral theorem and all other results remain unchange
H-theorem for classical matter around a black hole
We propose a classical solution for the kinetic description of matter falling
into a black hole, which permits to evaluate both the kinetic entropy and the
entropy production rate of classical infalling matter at the event horizon. The
formulation is based on a relativistic kinetic description for classical
particles in the presence of an event horizon. An H-theorem is established
which holds for arbitrary models of black holes and is valid also in the
presence of contracting event horizons
On the hyperbolicity and causality of the relativistic Euler system under the kinetic equation of state
We show that a pair of conjectures raised in [11] concerning the construction
of normal solutions to the relativistic Boltzmann equation are valid. This
ensures that the results in [11] hold for any range of positive temperatures
and that the relativistic Euler system under the kinetic equation of state is
hyperbolic and the speed of sound cannot overcome .Comment: 6 pages. Abridged version; full version to appear in Commun. Pure
Appl. Ana
Geometric structure of the generic static traversable wormhole throat
Traversable wormholes have traditionally been viewed as intrinsically
topological entities in some multiply connected spacetime. Here, we show that
topology is too limited a tool to accurately characterize a generic traversable
wormhole: in general one needs geometric information to detect the presence of
a wormhole, or more precisely to locate the wormhole throat. For an arbitrary
static spacetime we shall define the wormhole throat in terms of a
2-dimensional constant-time hypersurface of minimal area. (Zero trace for the
extrinsic curvature plus a "flare-out" condition.) This enables us to severely
constrain the geometry of spacetime at the wormhole throat and to derive
generalized theorems regarding violations of the energy conditions-theorems
that do not involve geodesic averaging but nevertheless apply to situations
much more general than the spherically symmetric Morris-Thorne traversable
wormhole. [For example: the null energy condition (NEC), when suitably weighted
and integrated over the wormhole throat, must be violated.] The major technical
limitation of the current approach is that we work in a static spacetime-this
is already a quite rich and complicated system.Comment: 25 pages; plain LaTeX; uses epsf.sty (four encapsulated postscript
figures
Inhomogeneous High Frequency Expansion-Free Gravitational Waves
We describe a natural inhomogeneous generalization of high frequency plane
gravitational waves. The waves are high frequency waves of the Kundt type whose
null propagation direction in space-time has vanishing expansion, twist and
shear but is not covariantly constant. The introduction of a cosmological
constant is discussed in some detail and a comparison is made with high
frequency gravity waves having wave fronts homeomorphic to 2-spheres.Comment: 18 pages, Latex file, accepted for publication in Physical Review
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