905 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.
Self sustained traversable wormholes and the equation of state
We compute the graviton one loop contribution to a classical energy in a
\textit{traversable} wormhole background. The form of the shape function
considered is obtained by the equation of state . We investigate
the size of the wormhole as a function of the parameter . The
investigation is evaluated by means of a variational approach with Gaussian
trial wave functionals. A zeta function regularization is involved to handle
with divergences. A renormalization procedure is introduced and the finite one
loop energy is considered as a \textit{self-consistent} source for the
traversable wormhole.The case of the phantom region is briefly discussed.Comment: Uses RevTeX 4. 21 pages. Submitted to Classical and Quantum Gravity.
Extended version of the talk given at ERE2006 (Palma de Mallorca, September
4-8, 2006) and of the talk given at MG11-GT5, Berlin, 23-29 July, 200
The Cosmological Constant as an Eigenvalue of a Sturm-Liouville Problem and its Renormalization
We discuss the case of massive gravitons and their relation with the
cosmological constant, considered as an eigenvalue of a Sturm-Liouville
problem. A variational approach with Gaussian trial wave functionals is used as
a method to study such a problem. We approximate the equation to one loop in a
Schwarzschild background and a zeta function regularization is involved to
handle with divergences. The regularization is closely related to the
subtraction procedure appearing in the computation of Casimir energy in a
curved background. A renormalization procedure is introduced to remove the
infinities together with a renormalization group equation.Comment: 8 pages, Talk given at "QFEXT'05", the 7-th workshop on quantum field
theory under the influence of external conditions, Barcelona, Spain, Sept.
5-9, 200
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
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
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
Black hole pair creation and the stability of flat space
We extend the Gross-Perry-Yaffe approach of hot flat space instability to
Minkowski space. This is done by a saddle point approximation of the partition
function in a Schwarzschild wormhole background which is coincident with an
eternal black hole. The appearance of an instability in the whole manifold is
here interpreted as a black hole pair creation.Comment: 11 pages,RevTeX4, 2 figures. Accepted for publication in Int. J. Mod.
Phys.
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.
Extracting the Cosmological Constant from the Wheeler DeWitt Equation in a Modified Gravity Theory
We discuss how to extract information about the cosmological constant from
the Wheeler-DeWitt equation, considered as an eigenvalue of a Sturm-Liouville
problem. A generalization to a f(R)theory is taken under examination. The
equation is approximated to one loop with the help of a variational approach
with Gaussian trial wave functionals. We use a zeta function regularization to
handle with divergences. A renormalization procedure is introduced to remove
the infinities together with a renormalization group equation.Comment: Talk given at QFEXT 07, Workshop on Quantum Field Theory Under the
Influence of External Conditions, Leipzig, 17-21 Sep 2007 and talk given at
9th International Conference on Path Integrals - New Trends and Perspectives,
Dresden, 23-28 September 2007. 8 pages, accepted for publication in Journal
of Physics
Phantom stars and topology change
In this work, we consider time-dependent dark energy star models, with an
evolving parameter crossing the phantom divide, . Once in
the phantom regime, the null energy condition is violated, which physically
implies that the negative radial pressure exceeds the energy density.
Therefore, an enormous negative pressure in the center may, in principle, imply
a topology change, consequently opening up a tunnel and converting the dark
energy star into a wormhole. The criteria for this topology change are
discussed, in particular, we consider the Morse Index analysis and a Casimir
energy approach involving quasi-local energy difference calculations that may
reflect or measure the occurrence of a topology change. We denote these exotic
geometries consisting of dark energy stars (in the phantom regime) and phantom
wormholes as phantom stars. The final product of this topological change,
namely, phantom wormholes, have far-reaching physical and cosmological
implications, as in addition to being used for interstellar shortcuts, an
absurdly advanced civilization may manipulate these geometries to induce closed
timelike curves, consequently violating causality.Comment: 19 pages, 13 figures. V2: Extended version of the paper accepted for
publication in Physical Review
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