713 research outputs found
Dark Energy and Viscous Cosmology
Singularities in the dark energy universe are discussed, assuming that there
is a bulk viscosity in the cosmic fluid. In particular, it is shown how the
physically natural assumption of letting the bulk viscosity be proportional to
the scalar expansion in a spatially flat FRW universe can drive the fluid into
the phantom region (w -1)
in the non-viscous case.Comment: 11 pages. Printing error in eq.(23) corrected. To appear in Gen. Rel.
Gra
Finite action, holographic conformal anomaly and quantum brane-worlds in d5 gauged supergravity
We report our recent results concerning d5 gauged supergravity (dilatonic
gravity) considered on AdS background. The finite action on such background as
well as d4 holographic conformal anomaly (via AdS/CFT correspondence) are
found. In such formalism the bulk potential is kept to be arbitrary, dilaton
dependent function. Holographic RG in such theory is briefly discussed. d5 AdS
brane-world Universe induced by quantum effects of brane CFT is constructed.
Such brane is spherical, hyperbolic or flat one. Hence, the possibility of
quantum creation of inflationary brane-world Universe is shown.Comment: Proceedings of Londrina conference, April 2000, to appea
Unified approach to study quantum properties of primordial black holes, wormholes and of quantum cosmology
We review the anomaly induced effective action for dilaton coupled spinors
and scalars in large N and s-wave approximation. It may be applied to study the
following fundamental problems: construction of quantum corrected black holes
(BHs), inducing of primordial wormholes in the early Universe (this effect is
confirmed) and the solution of initial singularity problem. The recently
discovered anti-evaporation of multiple horizon BHs is discussed. The existance
of such primordial BHs may be interpreted as SUSY manifestation. Quantum
corrections to BHs thermodynamics maybe also discussed within such scheme.Comment: LaTeX file and two eps files, to appear in MPLA, Brief Review
Supersymmetric new brane-world
The quantum-induced dilatonic brane world (New Brane World) is created by
brane CFT quantum effects (giving effective brane tension) in accordance with
AdS/CFT set-up which also defines surface term. Considering the bosonic sector
of 5d gauged supergravity with single scalar and taking the boundary action as
predicted by supersymmetry, the possibility to supersymmetrize dilatonic New
Brane World is discussed. It is demonstrated that for a number of
superpotentials the flat SUSY dilatonic brane-world (with dynamically induced
brane dilaton) or quantum-induced de Sitter dilatonic brane-world (not Anti-de
Sitter one) where SUSY is broken by the quantum effects occurs. The analysis of
graviton perturbations indicates that gravity is localized on such branes.Comment: LaTeX 16 pages, misprints are correcte
Effective Potential for D-brane in Constant Electromagnetic Field
We discuss the one-loop effective potential and static (large ) potential
for toroidal D-brane described by DBI-action in constant magnetic and in
constant electric fields. Explicit calculation is done for membrane case
() for both types of external fields and in case of static potential for
an arbitrary . In the case of one-loop potential it is found that the
presence of magnetic background may stabilize D-brane giving the possibility
for non-pointlike ground state configuration. On the same time, constant
electrical field acts against stabilization and the correspondent one-loop
potential is unbounded from below. The properties of static potential which
also has stable minimum are described in detail. The back-reaction of quantum
gauge fields to one-loop potential is also evaluated.Comment: LaTeX file,17 pages, few misprints and mistakes are correcte
Wightman function and vacuum densities for a Z_2-symmetric thick brane in AdS spacetime
Positive frequency Wightman function, vacuum expectation values of the field
square and the energy-momentum tensor induced by a Z_{2}-symmetric brane with
finite thickness located on (D+1)- dimensional AdS background are evaluated for
a massive scalar field with general curvature coupling parameter. For the
general case of static plane symmetric interior structure the expectation
values in the region outside the brane are presented as the sum of free AdS and
brane induced parts. For a conformally coupled massless scalar the brane
induced part in the vacuum energy-momentum tensor vanishes. In the limit of
strong gravitational fields the brane induced parts are exponentially
suppressed for points not too close to the brane boundary. As an application of
general results a special model is considered in which the geometry inside the
brane is a slice of the Minkowski spacetime orbifolded along the direction
perpendicular to the brane. For this model the Wightman function, vacuum
expectation values of the field square and the energy-momentum tensor inside
the brane are evaluated as well and their behavior is discussed in various
asymptotic regions of the parameters. It is shown that for both minimally and
conformally coupled scalar fields the interior vacuum forces acting on the
brane boundaries tend to decrease the brane thickness.Comment: 25 pages, 6 figures, discussion adde
Cosmological anti-deSitter space-times and time-dependent AdS/CFT correspondence
We study classes of five-dimensional cosmological solutions with negative
curvature, which are obtained from static solutions by an exchange of a spatial
and temporal coordinate, and in some cases by an analytic continuation. Such
solutions provide a suitable laboratory to address the time-dependent AdS/CFT
correspondence. For a specific example we address in detail the calculation of
the boundary stress-energy and the Wilson line and find disagreement with the
standard AdS/CFT correspondence. We trace these discrepancies to the
time-dependent effects, such as particle creation, which we further study for
specific backgrounds. We also identify specific time-dependent backgrounds that
reproduce the correct conformal anomaly. For such backgrounds the calculation
of the Wilson line in the adiabatic approximation indicates only a Coulomb
repulsion.Comment: LaTeX file, 47 pages, discussion is extended, version to appear in
PR
(Non) singular Kantowski-Sachs Universe from quantum spherically reduced matter
Using s-wave and large N approximation the one-loop effective action for 2d
dilaton coupled scalars and spinors which are obtained by spherical reduction
of 4d minimal matter is found. Quantum effective equations for reduced Einstein
gravity are written. Their analytical solutions corresponding to 4d
Kantowski-Sachs (KS) Universe are presented. For quantum-corrected Einstein
gravity we get non-singular KS cosmology which represents 1) quantum-corrected
KS cosmology which existed on classical level or 2)purely quantum solution
which had no classical limit. The analogy with Nariai BH is briefly mentioned.
For purely induced gravity (no Einstein term) we found general analytical
solution but all KS cosmologies under discussion are singular. The
corresponding equations of motion are reformulated as classical mechanics
problem of motion of unit mass particle in some potential V.Comment: LaTeX file, 16 pages, a few misprints are correcte
Vacuum densities for a thick brane in AdS spacetime
For a massive scalar field with general curvature coupling parameter we
evaluate Wightman function, vacuum expectation values of the field square and
the energy-momentum tensor induced by a -symmetric brane with finite
thickness located on -dimensional AdS bulk. For the general case of
static plane symmetric interior structure the expectation values in the region
outside the brane are presented as the sum of free AdS and brane induced parts.
For a conformally coupled massless scalar the brane induced part in the vacuum
energy-momentum tensor vanishes. In the limit of strong gravitational fields
the brane induced parts are exponentially suppressed for points not too close
to the brane boundary. As an application of general results a special model is
considered in which the geometry inside the brane is a slice of the Minkowski
spacetime orbifolded along the direction perpendicular to the brane. For this
model the Wightman function, vacuum expectation values of the field square and
the energy-momentum tensor inside the brane are evaluated. It is shown that for
both minimally and conformally coupled scalar fields the interior vacuum forces
acting on the brane boundaries tend to decrease the brane thickness.Comment: 12 pages, 2 figures, talk presented at QFEXT07, Leipzig, September
17-21, 200
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