739 research outputs found
Causal Structure of Vacuum Solutions to Conformal(Weyl) Gravity
Using Penrose diagrams the causal structure of the static spherically
symmetric vacuum solution to conformal (Weyl) gravity is investigated. A
striking aspect of the solution is an unexpected physical singularity at
caused by a linear term in the metric. We explain how to calculate the
deflection of light in coordinates where the metric is manifestly conformal to
flat i.e. in coordinates where light moves in straight lines.Comment: 18 pages, 2 figures, title and abstract changed, contents essentially
unaltered accepted for publication in General Relativity and Gravitatio
Brane Cosmology from Heterotic String Theory
We consider brane cosmologies within the context of five-dimensional actions
with O(a') higher curvature corrections. The actions are compatible with bulk
string amplitude calculations from heterotic string theory. We find wrapped
solutions that satisfy the field equations in an approximate but acceptable
manner given their complexity, where the internal four-dimensional scale factor
is naturally inflating, having an exponential De-Sitter form. The temporal
dependence of the metric components is non-trivial so that this metric cannot
be factored as in a conformally flat case. The effective Planck mass is finite
and the brane solutions localize four-dimensional gravity, while the
four-dimensional gravitational constant varies with time. The Hubble constant
can be freely specified through the initial value of the scalar field, to
conform with recent data.Comment: 15 pages, 3 figures, LaTeX, Accepted for Publication in IJT
Radiation from a Charge Uniformly Accelerated for All Time
A recent paper of Singal [Gen. Rel. Grav. 27 (1995), 953-967] argues that a
uniformly accelerated particle does not radiate, in contradiction to the
consensus of the research literature over the past 30 years. This note points
out some questionable aspects of Singal's argument and shows how similar
calculations can lead to the opposite conclusion.Comment: LaTeX, 9 pages, to appear in General Relativity and Gravitatio
Low-energy sector quantization of a massless scalar field outside a Reissner-Nordstrom black hole and static sources
We quantize the low-energy sector of a massless scalar field in the
Reissner-Nordstrom spacetime. This allows the analysis of processes involving
soft scalar particles occurring outside charged black holes. In particular, we
compute the response of a static scalar source interacting with Hawking
radiation using the Unruh (and the Hartle-Hawking) vacuum. This response is
compared with the one obtained when the source is uniformly accelerated in the
usual vacuum of the Minkowski spacetime with the same proper acceleration. We
show that both responses are in general different in opposition to the result
obtained when the Reissner-Nordstrom black hole is replaced by a Schwarzschild
one. The conceptual relevance of this result is commented.Comment: 12 pages (REVTEX), no figure
Rindler Particles and Classical Radiation
We describe the quantum and classical radiation by a uniformly accelerating
point source in terms of the elementary processes of absorption and emission of
Rindler scalar photons of the Fulling-Davies-Unruh bath observed by a
co-accelerating observer.To this end we compute the emission rate by a DeWitt
detector of a Minkowski scalar particle with defined transverse momentum per
unit of proper time of the source and we show that it corresponds to the
induced absorption or spontaneous and induced emission of Rindler photons from
the thermal bath. We then take what could be called the inert limit of the
DeWitt detector by considering the limit of zero gap energy. As suggested by
DeWitt, we identify in this limit the detector with a classical point source
and verify the consistency of our computation with the classical result.
Finally, we study the behavior of the emission rate in D space-time dimensions
in connection with the so called apparent statistics inversion.Comment: 8 pages, 2 figure
Asymptotic conservation laws in field theory
A new, general, field theoretic approach to the derivation of asymptotic
conservation laws is presented. In this approach asymptotic conservation laws
are constructed directly from the field equations according to a universal
prescription which does not rely upon the existence of Noether identities or
any Lagrangian or Hamiltonian formalisms. The resulting general expressions of
the conservation laws enjoy important invariance properties and synthesize all
known asymptotic conservation laws, such as the ADM energy in general
relativity.Comment: 13 pages, AMS-TeX, amsppt.sty, revised to give a better exposition
(we hope), and to correct some typesetting error
Path Integrals, Density Matrices, and Information Flow with Closed Timelike Curves
Two formulations of quantum mechanics, inequivalent in the presence of closed
timelike curves, are studied in the context of a soluable system. It
illustrates how quantum field nonlinearities lead to a breakdown of unitarity,
causality, and superposition using a path integral. Deutsch's density matrix
approach is causal but typically destroys coherence. For each of these
formulations I demonstrate that there are yet further alternatives in
prescribing the handling of information flow (inequivalent to previous
analyses) that have implications for any system in which unitarity or coherence
are not preserved.Comment: 25 pages, phyzzx, CALT-68-188
Dilaton Black Holes with Electric Charge
Static spherically symmetric solutions of the Einstein-Maxwell gravity with
the dilaton field are described. The solutions correspond to black holes and
are generalizations of the previously known dilaton black hole solution. In
addition to mass and electric charge these solutions are labeled by a new
parameter, the dilaton charge of the black hole. Different effects of the
dilaton charge on the geometry of space-time of such black holes are studied.
It is shown that in most cases the scalar curvature is divergent at the
horizons. Another feature of the dilaton black hole is that there is a finite
interval of values of electric charge for which no black hole can exist.Comment: 20 pages, LaTeX file + 1 figure, CALT-68-1885. (the postscript file
is improved
Higher derivative gravity with spontaneous symmetry breaking: Hamiltonian analysis of new covariant renormalizable gravity
In order to explore some general features of modified theories of gravity
which involve higher derivatives and spontaneous Lorentz and/or diffeomorphism
symmetry breaking, we study the recently proposed new version of covariant
renormalizable gravity (CRG). CRG attains power-counting renormalizability via
higher derivatives and introduction of a constrained scalar field and
spontaneous symmetry breaking. We obtain an Arnowitt-Deser-Misner
representation of the CRG action in four-dimensional spacetime with respect to
a foliation of spacetime adapted to the constrained scalar field. The resulting
action is analyzed by using Hamiltonian formalism. We discover that CRG
contains two extra degrees of freedom. One of them carries negative energy (a
ghost) and it will destabilize the theory due to its interactions. This result
is in contrast with the original paper [Phys. Lett. B 701, 117 (2011),
arXiv:1104.4286 [hep-th]], where it was concluded that the theory is free of
ghosts and renormalizable when we analyze fluctuations on the flat background.Comment: 39 pages. Presentation improved. Version published in Phys. Rev.
Radiation from the extremal black holes
The radiation from extreme Reissner-Nordstr\"{o}m black holes is computed by
explicitly considering the collapse of a spherical charged shell. No neutral
scalar radiation is found but there is emission of charged particles, provided
the charge to mass ratio be different from one. The absence of thermal effects
is in accord with the predictions of the euclidean theory but since the body
emits charged particles the entropy issue is not the same as for eternal
extreme black holes.Comment: 4 pages, LaTex, no figure
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