507 research outputs found
Domain Bubbles of Extra Dimensions
``Dimension bubbles'' of the type previously studied by Blau and Guendelman
[S.K. Blau and E.I. Guendelman, Phys. Rev. D40, 1909 (1989)], which effectively
enclose a region of 5d spacetime and are surrounded by a region of 4d
spacetime, can arise in a 5d theory with a compact extra dimension that is
dimensionally reduced to give an effective 4d theory. These bubbles with thin
domain walls can be stabilized against total collapse in a rather natural way
by a scalar field which, as in the case with ``ordinary'' nontopological
solitons, traps light scalar particles inside the bubble.Comment: 13 pages, no figures; to appear in Phys.Rev.
Fermionic and Bosonic Stabilizing Effects for Type I and Type II Dimension Bubbles
We consider two types of "dimension bubbles", which are viewed as 4d
nontopological solitons that emerge from a 5d theory with a compact extra
dimension. The size of the extra dimension varies rapidly within the domain
wall of the soliton. We consider the cases of type I (II) bubbles where the
size of the extra dimension inside the bubble is much larger (smaller) than
outside. Type I bubbles with thin domain walls can be stabilized by the
entrapment of various particle modes whose masses become much smaller inside
than outside the bubble. This is demonstrated here for the cases of scalar
bosons, fermions, and massive vector bosons, including both Kaluza-Klein zero
modes and Kaluza-Klein excitation modes. Type II bubbles expel massive particle
modes but both types can be stabilized by photons. Plasma filled bubbles
containing a variety of massless or nearly massless radiation modes may exist
as long-lived metastable states. Furthermore, in contrast to the case with a
"gravitational bag", the metric for a fluid-filled dimension bubble does not
exhibit a naked singularity at the bubble's center.Comment: 17 pages, no figs; to appear in Phys.Rev.
Junction Conditions of Friedmann-Robertson-Walker Space-Times
We complete a classification of junctions of two Friedmann-Robertson-Walker
space-times bounded by a spherical thin wall. Our analysis covers super-horizon
bubbles and thus complements the previous work of Berezin, Kuzumin and Tkachev.
Contrary to sub-horizon bubbles, various topology types for super-horizon
bubbles are possible, regardless of the sign of the extrinsic curvature. We
also derive a formula for the peculiar velocity of a domain wall for all types
of junction.Comment: 7 pages, LaTeX, figures are not included (available on request by
regular mail), WU-AP/31/9
Equation of motion for a domain wall coupled to gravitational field
The equation of motion for a domain wall coupled to gravitational field is
derived from the Nambu-Goto action. The domain wall is treated as a source of
gravitational field. The perturbed equation is also obtained with gravitational
back reaction on the wall motion taken into account. For general spherically
symmetric background case, the equation is expressed in terms of the
gauge-invariant variables.Comment: 13 pages, latex, no figures, uses REVTe
Inflation and Holography in String Theory
The encoding of an inflating patch of space-time in terms of a dual theory is
discussed. Following Bousso's interpretation of the holographic principle, we
find that those are generically described not by states in the dual theory but
by density matrices. We try to implement this idea on simple deformations of
the AdS/CFT examples, and an argument is given as to why inflation is so
elusive to string theory.Comment: 15 pages, LaTeX, 2 figures. Uses psbox.te
Modelling the dynamics of global monopoles
A thin wall approximation is exploited to describe a global monopole coupled
to gravity. The core is modelled by de Sitter space; its boundary by a thin
wall with a constant energy density; its exterior by the asymptotic
Schwarzschild solution with negative gravitational mass and solid angle
deficit, , where is the symmetry
breaking scale. The deficit angle equals when . We find that: (1) if , there exists a unique globally
static non-singular solution with a well defined mass, . provides
a lower bound on . If , the solution oscillates. There are no
inflating solutions in this symmetry breaking regime. (2) if ,
non-singular solutions with an inflating core and an asymptotically
cosmological exterior will exist for all . (3) if is not too large,
there exists a finite range of values of where a non-inflating monopole
will also exist. These solutions appear to be metastable towards inflation. If
is positive all solutions are singular. We provide a detailed description
of the configuration space of the model for each point in the space of
parameters, and trace the wall trajectories on both the interior
and the exterior spacetimes. Our results support the proposal that topological
defects can undergo inflation.Comment: 44 pages, REVTeX, 11 PostScript figures, submitted to the Physical
Review D. Abstract's correcte
Gauged Dimension Bubbles
Some of the peculiar electrodynamical effects associated with gauged
``dimension bubbles'' are presented. Such bubbles, which effectively enclose a
region of 5d spacetime, can arise from a 5d theory with a compact extra
dimension. Bubbles with thin domain walls can be stabilized against total
collapse by the entrapment of light charged scalar bosons inside the bubble,
extending the idea of a neutral dimension bubble to accommodate the case of a
gauged U(1) symmetry. Using a dielectric approach to the 4d dilaton-Maxwell
theory, it is seen that the bubble wall is almost totally opaque to photons,
leading to a new stabilization mechanism due to trapped photons. Photon
dominated bubbles very slowly shrink, resulting in a temperature increase
inside the bubble. At some critical temperature, however, these bubbles
explode, with a release of radiation.Comment: 14 pages, no figures; to appear in Phys.Rev.
Bubble wall perturbations coupled with gravitational waves
We study a coupled system of gravitational waves and a domain wall which is
the boundary of a vacuum bubble in de Sitter spacetime. To treat the system, we
use the metric junction formalism of Israel. We show that the dynamical degree
of the bubble wall is lost and the bubble wall can oscillate only while the
gravitational waves go across it. It means that the gravitational backreaction
on the motion of the bubble wall can not be ignored.Comment: 23 pages with 3 eps figure
dS/CFT correspondence on a brane
We study branes moving in an AdS Schwarzschild black hole background. When
the brane tension exceeds a critical value, the induced metric on the brane is
of FRW type and asymptotically de Sitter. We discuss the relevance of such
configurations to dS/CFT correspondence. When the black hole mass reaches a
critical value that depends on the brane tension, the brane interpolates in the
infinite past and future between a dS space and a finite space of zero Hubble
constant. This corresponds to a cosmological evolution without a Big Bang or a
Big Crunch. Moreover, the central charge of the CFT dual to the dS brane enters
the Cardy-Verlinde formula that gives the entropy of the thermal CFT dual to
the bulk AdS black hole.Comment: 15 pages, 1 figure, v2 references adde
Boundary Effects in Local Inflation and Spectrum of Density Perturbations
We observe that when a local patch in a radiation filled Robertson-Walker
universe inflates by some reason, outside perturbations can enter into the
inflating region. Generally, the physical wavelengths of these perturbations
become larger than the Hubble radius as they cross into the inflating space and
their amplitudes freeze out immediately. It turns out that the corresponding
power spectrum is not scale invariant. Although these perturbations cannot
reach out to a distance inner observer shielded by a de Sitter horizon, they
still indicate a curious boundary effect in local inflationary scenarios.Comment: 11 pages, 8 figures, revtex4, v4: minor typos corrected, twocolumn
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