397 research outputs found
Self-T-Dual Brane Cosmology
We show how T-duality can be implemented with brane cosmology. As a result,
we obtain a smooth bouncing cosmology with features similar to the ones of the
pre-Big Bang scenario. Also, by allowing T-duality transformations along the
time-like direction, we find a static solution that displays an interesting
self tuning property.Comment: 3 pages, based on a talk given at the XI Marcel Grossmann Meeting,
Berlin 23-29 July, 200
A new approach to non-commutative inflation
We propose an inflationary scenario inspired by a recent formulation, in
terms of coherent states, of non-commutative quantum field theory. We consider
the semiclassical Einstein equations, and we exploit the ultraviolet finiteness
of the non-commutative propagator to construct the expectation value of the
energy momentum tensor associated to a generic scalar field. It turns out that
the latter is always finite and dominated by an effective cosmological
constant. By combining this general feature with the intrinsic fuzziness of
spacetime, we show that non-commutativity governs the energy density of the
early Universe in such a way that the strong energy condition is violated.
Thus, there might be a bounce and a subsequent inflationary phase, which does
not need any \emph{ad hoc} scalar field.Comment: Version extended, more discussions and references, section added on
the cosmological constant, matches version accepted on Class. Quantum Gra
Black holes with non-minimal derivative coupling
We study the gravitational field equations in the presence of a coupling
between the derivative of a massless scalar field and the Einstein tensor. This
configuration is motivated by Galileon gravity as it preserves shift invariance
in the scalar sector. We analytically obtain solutions with static and
spherically symmetric geometry, which also include black holes with a single
regular horizon. We examine the thermodynamical properties of these solutions,
and we reveal the non-perturbative nature of the Galileon coupling constant. We
also find a phase transition, similar to the one described by Hawking and Page,
which occurs at a critical temperature determined by both the black hole mass
and by the strength of the coupling.Comment: Matches the published versio
Scale-invariant rotating black holes in quadratic gravity
Black hole solutions in pure quadratic theories of gravity are interesting
since they allow to formulate a set of scale-invariant thermodynamics laws.
Recently, we have proven that static scale-invariant black holes have a
well-defined entropy, which characterizes equivalent classes of solutions. In
this paper, we generalize these results and explore the thermodynamics of
rotating black holes in pure quadratic gravity.Comment: One typo corrected. Version accepted for publication in the "Entropy"
special issue: "Entropy in Quantum Gravity and Quantum Cosmology", editor R.
Garattin
Step-like discontinuities in Bose-Einstein condensates and Hawking radiation: dispersion effects
In this paper we extend the hydrodynamic results of [1] and study,
analytically, the propagation of Bogoliubov phonons on top of Bose-Einstein
condensates with step-like discontinuities by taking into account dispersion
effects. We focus on the Hawking signal in the density-density correlations in
the formation of acoustic black hole-like configurations.Comment: One figure and few comments added. Version accepted for publication
in PR
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