111 research outputs found
Inflating Brane inside hyper-spherically symmetric defects
Static and inflating brane world models are considered in -dimensions
with a non zero bulk cosmological constant and with a hyper-spherically
symmetric topological defect residing in the extra dimensions. Several
vacuum solutions can be constructed explicitely when the bulk and inflating
constants are non zero. We study how these solutions are deformed by the
presence of a global monopole for generic values of and a local monopole
for . New types of solutions, regular and periodic in the radial variable
relative to the extra dimensions, are constructed.Comment: 23 pages, 9 figures, results extended, references adde
New insights on the matter-gravity coupling paradigm
The coupling between matter and gravity in General Relativity is given by a
proportionality relation between the stress tensor and the geometry. This is an
oriented assumption driven by the fact that both the stress tensor and the
Einstein tensor are divergenceless. However, General Relativity is in essence a
nonlinear theory, so there is no obvious reason why the coupling to matter
should be linear. On another hand, modified theories of gravity usually affect
the vacuum dynamics, yet keep the coupling to matter linear. In this Letter we
address the implications of consistent nonlinear gravity/matter coupling. The
Eddington inspired Born-Infeld theory recently introduced by Banados and
Ferreira provides an enlightening realization of such coupling modifications.
We find that this theory coupled to a perfect fluid reduces to General
Relativity coupled to a nonlinearly modified perfect fluid, leading to an
ambiguity between modified coupling and modified equation of state. We discuss
observational consequences of this degeneracy and argue that such a completion
of General Relativity is viable from both an experimental and theoretical point
of view through energy conditions, consistency, and singularity-avoidance
perspectives. We use these results to discuss the impact of changing the
coupling paradigm.Comment: 6 pages, 2 figures, v2: revised version, v3: published versio
Non Uniform Black Strings and Critical Dimensions in
We study the equations of black strings in spacetimes of arbitrary dimensions
with a negative cosmological constant and construct numerically non uniform
black strings solutions. Our results suggest the existence of a localised black
hole in asymptotically locally spacetime. We also present evidences for a
dependence of the critical dimension on the horizon radius.The critical
dimension represents the dimension where the order of the phase transition
between uniform and non uniform black string changes. Finally, we argue that
both, the regular asymptotically locally solution and black string
solutions with a very small horizon radius, present a negative tension. This
turns out to be an unexpected feature of the solutions.Comment: 13 pages, 5 figure
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