799 research outputs found
The cosmological constant as an eigenvalue of the Hamiltonian constraint in Horava-Lifshits theory
In the framework of Horava-Lifshitz theory, we study the eigenvalues
associated with the Wheeler-DeWitt equation representing the vacuum expectation
values associated with the cosmological constant. The explicit calculation is
performed with the help of a variational procedure with trial wave functionals
of the Gaussian type. We analyze both the case with the detailed balanced
condition and the case without it. In the case without the detailed balance, we
find the existence of an eigenvalue depending on the set of coupling constants
(g2,g3) and (g4,g5,g6), respectively, and on the physical scale.Comment: RevTeX,11 Pages, Substantial Improvements. References added. To
appear in Phys.Rev.
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
Space Time Foam: a ground state candidate for Quantum Gravity
A model of space-time foam, made by wormholes is considered. The Casimir
energy leading to such a model is computed by means of the phase shift method
which is in agreement with the variational approach used in Refs.[9-14]. The
collection of Schwarzschild and Reissner-Nordstr\"{o}m wormholes are separately
considered to represent the foam. The Casimir energy shows that the
Reissner-Nordstr\"{o}m wormholes cannot be used to represent the foam.Comment: 6 pages.RevTeX with package epsf and two eps figures. To be submitted
to the proceedings of the 4th Workshop of `Mysteries, Puzzles And Paradoxes
In Quantum Mechanics' Gargnano (Italy), 27 August-1 September 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
Naked Singularity in a Modified Gravity Theory
The cosmological constant induced by quantum fluctuation of the graviton on a
given background is considered as a tool for building a spectrum of different
geometries. In particular, we apply the method to the Schwarzschild background
with positive and negative mass parameter. In this way, we put on the same
level of comparison the related naked singularity (-M) and the positive mass
wormhole. We discuss how to extract information in the context of a f(R)
theory. We use the Wheeler-De Witt equation as a basic equation to perform such
an analysis regarded as a Sturm-Liouville problem . The application of the same
procedure used for the ordinary theory, namely f(R)=R, reveals that to this
approximation level, it is not possible to classify the Schwarzschild and its
naked partner into a geometry spectrum.Comment: 8 Pages. Contribution given to DICE 2008. To appear in the
proceeding
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