58 research outputs found
Cosmological k-essence condensation
We consider a model of dark energy/matter unification based on a k-essence
type of theory similar to tachyon condensate models. Using an extension of the
general relativistic spherical model which incorporates the effects of both
pressure and the acoustic horizon we show that an initially perturbative
k-essence fluid evolves into a mixed system containing cold dark matter like
gravitational condensate in significant quantities.Comment: 8 pages, 2 figures, presented by NB at the conference Beyond 2010,
Cape Town, 1-6 February 201
Gravitational Phase Transition of Fermionic Matter in a General-Relativistic Framework
The Thomas-Fermi model at finite temperature is extended to describe a system
of self-gravitating weakly interacting massive fermions in a
general-relativistic framework. By cooling a nondegenerate gas of weakly
interacting massive fermions below some critical temperature, a condensed phase
emerges, consisting of quasidegenerate fermion stars. For fermion masses of 10
to 25 keV, these fermion stars may very well provide an alternative explanation
for the supermassive compact dark objects that are observed at galactic
centers.Comment: 19 pages incl. 8 ps-figs, LaTe
Gauges in the Bulk II: Models with Bulk Scalars
Extending previous work in Randall-Sundrum type models, we construct
low-energy effective actions for braneworlds with a bulk scalar field, with
special attention to the case of BPS branes. Holding the branes at fixed
coordinate position with a general ansatz for the bulk metric, and imposing the
Einstein frame as a gauge condition, we obtain a scalar-tensor theory with only
one scalar degree of freedom related to the proper brane separation. The
formalism is applicable even when there is direct coupling of the bulk scalar
and brane matter, as in the Horava-Witten model. We further show that the usual
moduli space approximation actually describes a non-BPS three-brane system.Comment: LaTeX file of 18 page
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