985 research outputs found
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
Gravity's Rainbow induces Topology Change
In this work, we explore the possibility that quantum fluctuations induce a
topology change, in the context of Gravity's Rainbow. A semi-classical approach
is adopted, where the graviton one-loop contribution to a classical energy in a
background spacetime is computed through a variational approach with Gaussian
trial wave functionals. The energy density of the graviton one-loop
contribution, or equivalently the background spacetime, is then let to evolve,
and consequently the classical energy is determined. More specifically, the
background metric is fixed to be Minkowskian in the equation governing the
quantum fluctuations, which behaves essentially as a backreaction equation, and
the quantum fluctuations are let to evolve; the classical energy, which depends
on the evolved metric functions, is then evaluated. Analysing this procedure, a
natural ultraviolet (UV) cutoff is obtained, which forbids the presence of an
interior spacetime region, and may result in a multipy-connected spacetime.
Thus, in the context of Gravity's Rainbow, this process may be interpreted as a
change in topology, and in principle results in the presence of a Planckian
wormhole.Comment: Updated to match published version. The "Topology Change" section has
been revised introducing a connection with the "Ricci flow". RevTeX4, 13
Page
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
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
Casimir energy and variational methods in AdS spacetime
Following the subtraction procedure for manifolds with boundaries, we
calculate by variational methods, the Schwarzschild-Anti-de Sitter and the
Anti-de Sitter space energy difference. By computing the one loop approximation
for TT tensors we discover the existence of an unstable mode at zero
temperature, which can be stabilized by the boundary reduction method.
Implications on a foam-like space are discussed.Comment: Submitted to Classical and Quantum Gravit
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