646 research outputs found
Dynamics of the Fisher Information Metric
We present a method to generate probability distributions that correspond to
metrics obeying partial differential equations generated by extremizing a
functional , where is the
Fisher metric. We postulate that this functional of the dynamical variable
is stationary with respect to small variations of these
variables. Our approach enables a dynamical approach to Fisher information
metric. It allows to impose symmetries on a statistical system in a systematic
way. This work is mainly motivated by the entropy approach to nonmonotonic
reasoning.Comment: 11 page
Empirical constraints on vacuum decay in the stringy landscape
It is generally considered as self evident that the lifetime of our vacuum in
the landscape of string theory cannot be much shorter than the current age of
the universe. Here I show why this lower limit is invalid. A certain type of
``parallel universes'' is a necessary consequence of the string-landscape
dynamics and might well allow us to ``survive'' vacuum decay. As a consequence
our stringy vacuum's lifetime is empirically unconstrained and could be very
short. Based on this counter-intuitive insight I propose a novel type of
laboratory experiment that searches for an apparent violation of the
quantum-mechanical Born rule by gravitational effects on vacuum decay. If the
lifetime of our vacuum should turn out to be shorter than 6 x 10^{-13} seconds
such an experiment is sufficiently sensitive to determine its value with
state-of-the-art equipment.Comment: 13 pages, 2 figures, proposes a laboratory experimen
Alternative derivation of the relativistic contribution to perihelic precession
An alternative derivation of the first-order relativistic contribution to
perihelic precession is presented. Orbital motion in the Schwarzschild geometry
is considered in the Keplerian limit, and the orbit equation is derived for
approximately elliptical motion. The method of solution makes use of coordinate
transformations and the correspondence principle, rather than the standard
perturbative approach. The form of the resulting orbit equation is similar to
that derived from Newtonian mechanics and includes first-order corrections to
Kepler's orbits due to general relativity. The associated relativistic
contribution to perihelic precession agrees with established first-order
results. The reduced radius for the circular orbit is in agreement to
first-order with that calculated from the Schwarzschild effective potential.
The method of solution is understandable by undergraduate students.Comment: 12 pages, 2 figures. Accepted for publication in the American Journal
of Physic
Removing black-hole singularities with nonlinear electrodynamics
We propose a way to remove black hole singularities by using a particular
nonlinear electrodynamics Lagrangian that has been recently used in various
astrophysics and cosmological frameworks. In particular, we adapt the
cosmological analysis discussed in a previous work to the black hole physics.
Such analysis will be improved by applying the Oppenheimer-Volkoff equation to
the black hole case. At the end, fixed the radius of the star, the final
density depends only on the introduced quintessential density term
and on the mass.Comment: In this last updated version we correct two typos which were present
in Eqs. (21) and (22) in the version of this letter which has been published
in Mod. Phys. Lett. A 25, 2423-2429 (2010). In the present version, both of
Eqs. (21) and (22) are dimensionally and analytically correc
Wormholes as Black Hole Foils
We study to what extent wormholes can mimic the observational features of
black holes. It is surprisingly found that many features that could be thought
of as ``characteristic'' of a black hole (endowed with an event horizon) can be
closely mimicked by a globally static wormhole, having no event horizon. This
is the case for: the apparently irreversible accretion of matter down a hole,
no-hair properties, quasi-normal-mode ringing, and even the dissipative
properties of black hole horizons, such as a finite surface resistivity equal
to 377 Ohms. The only way to distinguish the two geometries on an
observationally reasonable time scale would be through the detection of
Hawking's radiation, which is, however, too weak to be of practical relevance
for astrophysical black holes. We point out the existence of an interesting
spectrum of quantum microstates trapped in the throat of a wormhole which could
be relevant for storing the information ``lost'' during a gravitational
collapse.Comment: 13 pages, no figures, Late
Active gravitational mass and the invariant characterization of Reissner-Nordstrom spacetime
We analyse the concept of active gravitational mass for Reissner-Nordstrom
spacetime in terms of scalar polynomial invariants and the Karlhede
classification. We show that while the Kretschmann scalar does not produce the
expected expression for the active gravitational mass, both scalar polynomial
invariants formed from the Weyl tensor, and the Cartan scalars, do.Comment: 6 pages Latex, to appear in General Relativity and Gravitatio
Newton-Hooke spacetimes, Hpp-waves and the cosmological constant
We show explicitly how the Newton-Hooke groups act as symmetries of the
equations of motion of non-relativistic cosmological models with a cosmological
constant. We give the action on the associated non-relativistic spacetimes and
show how these may be obtained from a null reduction of 5-dimensional
homogeneous pp-wave Lorentzian spacetimes. This allows us to realize the
Newton-Hooke groups and their Bargmann type central extensions as subgroups of
the isometry groups of the pp-wave spacetimes. The extended Schrodinger type
conformal group is identified and its action on the equations of motion given.
The non-relativistic conformal symmetries also have applications to
time-dependent harmonic oscillators. Finally we comment on a possible
application to Gao's generalization of the matrix model.Comment: 21 page
SHORTCUT METHOD OF SOLUTION OF GEODESIC EQUATIONS FOR SCHWARZSCHILD BLACK HOLE
It is shown how the use of the Kerr-Schild coordinate system can greatly
simplify the formulation of the geodesic equation of the Schwarzschild
solution. An application of this formulation to the numerical computation of
the aspect of a non-rotating black hole is presented. The generalization to the
case of the Kerr solution is presented too.Comment: 11 pages, 2 PostScript figures (available as uuencoded compressed tar
file), uses epsfig.tex). Accepted on February 1995 for publication in
Classical and Quantum Gravit
The Interaction Of Multiple Convection Zones In A-type Stars
A-type stars have a complex internal structure with the possibility of
multiple convection zones. If not sufficiently separated, such zones will
interact through the convectively stable regions that lie between them. It is
therefore of interest to ask whether the typical conditions that exist within
such stars are such that these convections zones can ever be considered as
disjoint.
In this paper we present results from numerical simulations that help in
understanding how increasing the distance between the convectively unstable
regions are likely to interact through the stable region that separates them.
This has profound implications for mixing and transport within these stars.Comment: 9 pages, 15 figures, Preprint accepted for publication in MNRA
Kerr black holes in horizon-generating form
New coordinates are given which describe non-degenerate Kerr black holes in
dual-null foliations based on the outer (or inner) horizons, generalizing the
Kruskal form for Schwarzschild black holes. The construction involves an area
radius for the transverse surfaces and a generalization of the Regge-Wheeler
radial function, both functions of the original radial coordinate only.Comment: 4 revtex4 page
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