692 research outputs found
What Casimir Energy can suggest about Space Time Foam?
In the context of a model of space-time foam, made by wormholes we
discuss the possibility of having a foam formed by different configurations. An
equivalence between Schwarzschild and Schwarzschild-Anti-de Sitter wormholes in
terms of Casimir energy is shown. An argument to discriminate which
configuration could represent a foamy vacuum coming from Schwarzschild black
hole transition frequencies is used. The case of a positive cosmological
constant is also discussed. Finally, a discussion involving charged wormholes
leads to the conclusion that they cannot be used to represent a ground state of
the foamy type.Comment: ReVTeX, 3 pages. Talk given at the Fifth Workshop on Quantum Field
Theory under the Influence of External Conditions, Leipzig, September 10-14,
200
The cosmological constant as an eigenvalue of f(R)-gravity Hamiltonian constraint
In the framework of ADM formalism, it is possible to find out eigenvalues of
the WDW equation with the meaning of vacuum states, i.e. cosmological
constants, for f(R) theories of gravity, where f(R) is a generic analytic
function of the Ricci curvature scalar R. The explicit calculation is performed
for a Schwarzschild metric where one-loop energy is derived by the zeta
function regularization method and a renormalized running Lambda constant is
obtained.Comment: 16 pages, to appear in Class. Quant. Gra
New instabilities of de Sitter spacetimes
We construct an instanton describing the pair production of non-Kaluza Klein
bubbles of nothing in higher odd dimensional de Sitter spaces. In addition to
showing that higher dimensional de Sitter spaces have a nonzero probability to
become topologically nontrivial, this process provides direct evidence for the
association of entropy with cosmological horizons and that non-Kaluza Klein
bubbles of nothing are a necessary ingredient in string theory or any other
consistent quantum theory of gravity in higher dimensions.Comment: 19 pages, 1 figur
Casimir energy and black hole pair creation in Schwarzschild-de Sitter spacetime
Following the subtraction procedure for manifolds with boundaries, we
calculate by variational methods, the Schwarzschild-de Sitter and the de Sitter
space energy difference. By computing the one loop approximation for TT tensors
we discover the existence of an unstable mode even for the non-degenerate case.
This result seems to be in agreement with the sub-maximal black hole pair
creation of Bousso-Hawking. The instability can be eliminated by the boundary
reduction method. Implications on a foam-like space are discussed.Comment: 19 pages,RevTeX with package epsf and four eps figures. Added other
references. Accepted for publication in Classical and Quantum Gravit
Particle propagation and effective space-time in Gravity's Rainbow
Basing on the results obtained in a our previous study on Gravity's Rainbow,
we determine the quantum corrections to the space-time metric for the
Schwarzschild and the de Sitter background, respectively. We analyze how
quantum fluctuations alter these metrics inducing modifications on the
propagation of test particles. Significantly enough we find that quantum
corrections can become relevant not only for particles approaching the Planck
energy but, due to the one loop contribution, even for low-energy particles as
far as Planckian length scales are considered. We briefly compare our results
with others obtained in similar studies and with the recent experimental OPERA
announcement of superluminal neutrino propagation.Comment: RevTeX 4, 11 page
Spacetime Foam Model of the Schwarzschild Horizon
We consider a spacetime foam model of the Schwarzschild horizon, where the
horizon consists of Planck size black holes. According to our model the entropy
of the Schwarzschild black hole is proportional to the area of its event
horizon. It is possible to express geometrical arguments to the effect that the
constant of proportionality is, in natural units, equal to one quarter.Comment: 16 pages, 2 figures, improved and extended version with some
significant changes. Accepted for publication in Phys.Rev.
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