128 research outputs found
Vacuum and semiclassical gravity: a difficulty and its bewildering significance
We review a long-standing difficulty in some semiclassical models of vacuum
and vacuum decay. Surprisingly enough these models, careless of their
transparent formulation, are affected by, both, technical and conceptual
issues. After proving some general results that are relevant for, both, the
Euclidean and Lorentzian sectors of their dynamics, we briefly highlight their
importance in connection with the issues discussed before, arguing that their
solution might be interesting in our quest for quantum gravity.Comment: 11 pages, LaTeX, 4 figure; talk given at the workshop "From Quantum
to Emergent Gravity: Theory and Phenomenology", June, 11-15 2007, Trieste,
Italy (http://www.sissa.it/app/QGconference); submitted to the "Proceedings
of Science" (http://pos.sissa.it
Minisuperspace, WKB, Quantum States of General Relativistic Extended Objects
The dynamics of relativistic thin shells is a recurrent topic in the
literature about the classical theory of gravitating systems and the still
ongoing attempts to obtain a coherent description of their quantum behavior.
Certainly, a good reason to make this system a preferred one for many models is
the clear, synthetic description given by Israel junction conditions. Using
some results from an effective Lagrangian approach to the dynamics of
spherically symmetric shells, we show a general way to obtain WKB states for
the system; a simple example is also analyzed.Comment: 3 pages, to appear in the proceedings of the 16th SIGRAV conference
on general relativity and gravitational physic
Braneworlds and Quantum States of Relativistic Shells
We review some applications of relativistic shells that are relevant in the
context of quantum gravity/quantum cosmology. Using a recently developed
approach, the stationary states of this general relativistic system can be
determined in the semiclassical approximation. We suggest that this technique
might be of phenomenological relevance in the context of the brane-world
scenario and we draw a picture of the general set-up and of the possible
developments.Comment: 4 pages, LaTeX. To appear in the proceedings of the Eleventh Marcel
Grossmann Meeting on General Relativity, July 23-29, 2006, Freie Universitaet
Berlin, Berlin, Germany (http://www.icra.it/mg/mg11
WKB metastable quantum states of a de Sitter--Reissner-Nordstroem dust shell
We study the dynamics of a spherically symmetric dust shell separating two
spacetime domains, the 'interior' one being a part of the de Sitter spacetime
and the exterior one having the 'extremal' Reissner-Nordstroem geometry.
Extending the ideas of previous works on the subject, we show that the it is
possible to determine the (metastable) WKB quantum states of this gravitational
system.Comment: IOPart class, 16 figure
Unified Dark Energy-Dark Matter model with Inverse Quintessence
We consider a model where both dark energy and dark matter originate from the
coupling of a scalar field with a non-conventional kinetic term to, both, a
metric measure and a non-metric measure. An interacting dark energy/dark matter
scenario can be obtained by introducing an additional scalar that can produce
non constant vacuum energy and associated variations in dark matter. The
phenomenology is most interesting when the kinetic term of the additional
scalar field is ghost-type, since in this case the dark energy vanishes in the
early universe and then grows with time. This constitutes an "inverse
quintessence scenario", where the universe starts from a zero vacuum energy
density state, instead of approaching it in the future.Comment: 13 pages; minor changes with references adde
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