732 research outputs found
Necessary Dependence of Currents on Fields They Generate
It is shown that in local (proper) Lorentz-invariant theories involving axial-vector, or tensor currents (conserved or not), the latter must vanish, if they commute at equal times with the fields they generate. The need for explicit field dependence of currents is demonstrated for gradient-coupled spinless and massive spin-one fields, as well as for electrodynamics with minimal or nonminimal coupling. The field-dependence requirement is distinct from that (already needed for free fields) of "spreading points" to make the current operators well-defined. The relation between the two, however, essentially fixes the form of this dependence. Applications are made to partially conserved currents, â_ÎŒ^ÎŒ = αÏ; if j^0 commutes with Ï, the latter vanishes
Charged gravitational instantons in five-dimensional Einstein-Gauss-Bonnet-Maxwell theory
We study a solution of the Einstein-Gauus-Bonnet theory in 5 dimensions
coupled to a Maxwell field, whose euclidean continuation gives rise to an
instanton describing black hole pair production. We also discuss the dual
theory with a 3-form field coupled to gravity.Comment: 8 pages, plain Te
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
On the variable-charged black holes embedded into de Sitter space: Hawking's radiation
In this paper we study the Hawking evaporation of masses of variable-charged
Reissner-Nordstrom and Kerr-Newman, black holes embedded into the de Sitter
universe by considering the charge to be function of radial coordinate of the
spherically symmetric metric.Comment: LaTex, p. 2
On the instability of classical dynamics in theories with higher derivatives
The development of instability in the dynamics of theories with higher
derivatives is traced in detail in the framework of the Pais-Uhlenbeck fourth
oder oscillator. For this aim the external friction force is introduced in the
model and the relevant solutions to equations of motion are investigated. As a
result, the physical implication of the energy unboundness from below in
theories under consideration is revealed.Comment: 9 pages, no figures and no tables, revtex4; a few misprints are
correcte
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
Interaction of Hawking radiation with static sources outside a Schwarzschild black hole
We show that the response rate of (i) a static source interacting with
Hawking radiation of massless scalar field in Schwarzschild spacetime (with the
Unruh vacuum) and that of (ii) a uniformly accelerated source with the same
proper acceleration in Minkowski spacetime (with the Minkowski vacuum) are
equal. We show that this equality will not hold if the Unruh vacuum is replaced
by the Hartle-Hawking vacuum. It is verified that the source responds to the
Hawking radiation near the horizon as if it were at rest in a thermal bath in
Minkowski spacetime with the same temperature. It is also verified that the
response rate in the Hartle-Hawking vacuum approaches that in Minkowski
spacetime with the same temperature far away from the black hole. Finally, we
compare our results with others in the literature.Comment: 18 pages (REVTEX
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
Consistency of Semiclassical Gravity
We discuss some subtleties which arise in the semiclassical approximation to
quantum gravity. We show that integrability conditions prevent the existence of
Tomonaga-Schwinger time functions on the space of three-metrics but admit them
on superspace. The concept of semiclassical time is carefully examined. We
point out that central charges in the matter sector spoil the consistency of
the semiclassical approximation unless the full quantum theory of gravity and
matter is anomaly-free. We finally discuss consequences of these considerations
for quantum field theory in flat spacetime, but with arbitrary foliations.Comment: 12 pages, LATEX, Report Freiburg THEP-94/2
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
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