12,327 research outputs found
Extended 2d generalized dilaton gravity theories
We show that an anomaly-free description of matter in (1+1) dimensions
requires a deformation of the 2d relativity principle, which introduces a
non-trivial center in the 2d Poincare algebra. Then we work out the reduced
phase-space of the anomaly-free 2d relativistic particle, in order to show that
it lives in a noncommutative 2d Minkowski space. Moreover, we build a Gaussian
wave packet to show that a Planck length is well-defined in two dimensions. In
order to provide a gravitational interpretation for this noncommutativity, we
propose to extend the usual 2d generalized dilaton gravity models by a specific
Maxwell component, which gauges the extra symmetry associated with the center
of the 2d Poincare algebra. In addition, we show that this extension is a high
energy correction to the unextended dilaton theories that can affect the
topology of space-time. Further, we couple a test particle to the general
extended dilaton models with the purpose of showing that they predict a
noncommutativity in curved space-time, which is locally described by a Moyal
star product in the low energy limit. We also conjecture a probable
generalization of this result, which provides a strong evidence that the
noncommutativity is described by a certain star product which is not of the
Moyal type at high energies. Finally, we prove that the extended dilaton
theories can be formulated as Poisson-Sigma models based on a nonlinear
deformation of the extended Poincare algebra.Comment: 21 pages, IOP LaTeX2e preprint classfile, Improved discussions, Minor
corrections, More didactic, More self-contained, New results concerning
noncommutativity in curved space-time, Accepted for publication in Classical
and Quantum Gravity on 02 Jul 200
Casimir Densities for a Massive Fermionic Quantum Field in a Global Monopole Background with Spherical Boundary
We investigate the vacuum expectation value of the energy-momentum tensor
associated with a massive fermionic field obeying the MIT bag boundary
condition on a spherical shell in the global monopole spacetime. The asymptotic
behavior of the vacuum densities is investigated near the sphere center and
surface, and at large distances from the sphere. In the limit of strong
gravitational field corresponding to small values of the parameter describing
the solid angle deficit in global monopole geometry, the sphere-induced
expectation values are exponentially suppressed.Comment: 8 pages, 4 figures, 6th Alexander Friedmann International Seminar on
Gravitation and Cosmolog
Vacuum polarization by topological defects in de Sitter spacetime
In this paper we investigate the vacuum polarization effects associated with
a massive quantum scalar field in de Sitter spacetime in the presence of
gravitational topological defects. Specifically we calculate the vacuum
expectation value of the field square, . Because this investigation
has been developed in a pure de Sitter space, here we are mainly interested on
the effects induced by the presence of the defects.Comment: Talk presented at the 1st. Mediterranean Conference on Classical and
Quantum Gravity (MCCQG
Nonplanar integrability at two loops
In this article we compute the action of the two loop dilatation operator on
restricted Schur polynomials that belong to the su(2) sector, in the displaced
corners approximation. In this non-planar large N limit, operators that
diagonalize the one loop dilatation operator are not corrected at two loops.
The resulting spectrum of anomalous dimensions is related to a set of decoupled
harmonic oscillators, indicating integrability in this sector of the theory at
two loops. The anomalous dimensions are a non-trivial function of the 't Hooft
coupling, with a spectrum that is continuous and starting at zero at large N,
but discrete at finite N.Comment: version to appear in JHE
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