181 research outputs found
Anti de Sitter Gravity from BF-Chern-Simons-Higgs Theories
It is shown that an action inspired from a BF and Chern-Simons model, based
on the isometry group SO(3, 2), with the inclusion of a Higgs potential
term, furnishes the MacDowell-Mansouri-Chamseddine-West action for gravity,
with a Gauss-Bonnet and cosmological constant term. The space is a
natural vacuum of the theory. Using Vasiliev's procedure to construct higher
spin massless fields in AdS spaces and a suitable star product, we discuss the
preliminary steps to construct the corresponding higher-spin action in
space representing the higher spin extension of this model. Brief remarks on
Noncommutative Gravity are made.Comment: 6 pages, plain Tex, Revised. References are are adde
The Partition Function for Topological Field Theories
We use a Hodge decomposition and its generalization to non-abelian flat
vector bundles to calculate the partition function for abelian and non- abelian
BF theories in dimensions. This enables us to provide a simple proof that
the partition function is related to the Ray-Singer torsion defined on flat
vector bundles for all odd-dimensional manifolds, and is equal to unity for
even dimensions.Comment: 23 pages, plain-TeX fil
Conformal and Nonconformal Symmetries in 2d Dilaton gravity
We study finite-dimensional extra symmetries of generic 2D dilaton gravity
models. Using a non-linear sigma model formulation we show that the unique
theories admitting an extra (conformal) symmetry are the models with an
exponential potential (), which include the CGHS
model as a particular though limiting () case. These models give rise
to black hole solutions with a mass-dependent temperature. The underlying extra
symmetry can be maintained in a natural way in the one-loop effective action,
thus implying the exact solubility of the semiclassical theory including
back-reaction. Moreover, we also introduce three different classes of
(non-conformal) transformations which are extra symmetries for generic 2D
dilaton gravity models. Special linear combinations of these transformations
turn out to be the (conformal) symmetries of the CGHS and models. We show that one of the non-conformal extra symmetries
can be converted into a conformal one by means of adequate field redefinitions
involving the metric and the derivatives of the dilaton. Finally, by expressing
the Polyakov-Liouville effective action in terms of an invariant metric, we are
able to provide semiclassical models which are also invariant. This generalizes
the solvable semiclassical model of Bose, Parker and Peleg (BPP) for a generic
2D dilaton gravity model.Comment: Latex, no figures. Revised version published i
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