2,120 research outputs found
Tachyon fields with effects of quantum matter in an Anti-de Sitter Universe
We consider an Anti-de Sitter universe filled by quantum conformal matter
with the contribution from the usual tachyon and a perfect fluid. The model
represents the combination of a trace-anomaly annihilated and a tachyon driven
Anti-de Sitter universe. The influence exerted by the quantum effects and by
the tachyon on the AdS space is studied. The radius corresponding to this
universe is calculated and the effect of the tachyon potential is discussed, in
particular, concerning to the possibility to get an accelerated scale factor
for the proposed model (implying an accelerated expansion of the AdS type of
universe). Fulfillment of the cosmological energy conditions in the model is
also investigatedComment: 14 Latex pages, no figure
Models for Little Rip Dark Energy
We examine in more detail specific models which yield a little rip cosmology,
i.e., a universe in which the dark energy density increases without bound but
the universe never reaches a finite-time singularity. We derive the conditions
for the little rip in terms of the inertial force in the expanding universe and
present two representative models to illustrate in more detail the difference
between little rip models and those which are asymptotically de Sitter. We
derive conditions on the equation of state parameter of the dark energy to
distinguish between the two types of models. We show that coupling between dark
matter and dark energy with a little rip equation of state can alter the
evolution, changing the little rip into an asymptotic de Sitter expansion. We
give conditions on minimally-coupled phantom scalar field models and on
scalar-tensor models that indicate whether or not they correspond to a little
rip expansion. We show that, counterintuitively, despite local instability, a
little-rip cosmology has an infinite lifetime.Comment: LaTeX, 10 pages, no figure, version to appear in Phys.Lett
Holographic entropy and brane FRW-dynamics from AdS black hole in d5 higher derivative gravity
Higher derivative bulk gravity (without Riemann tensor square term) admits
AdS-Schwarzschild black hole as exact solution. It is shown that induced brane
geometry on such background is open, flat or closed FRW radiation dominated
Universe. Higher derivative terms contributions appear in the Hawking
temperature, entropy and Hubble parameter via the redefinition of 5-dimensional
gravitational constant and AdS scale parameter. These higher derivative terms
do not destroy the AdS-dual description of radiation represented by
strongly-coupled CFT. Cardy-Verlinde formula which expresses cosmological
entropy as square root from other parameters and entropies is derived in
gravity. The corresponding cosmological entropy bounds are briefly discussed.Comment: LaTeX file, 19 page
Cosmological solutions in F(R) Horava-Lifshitz gravity
At the present work, it is studied the extension of F (R) gravities to the
new recently proposed theory of gravity, the so-called Horava-Lifshitz gravity,
which provides a way to make the theory power counting renormalizable by
breaking Lorentz invariance. It is showed that dark energy can be well
explained in the frame of this extension, just in terms of gravity. It is also
explored the possibility to unify inflation and late-time acceleration under
the same mechanism, providing a natural explanation the accelerated expansion.Comment: 4 pages. Contribution to the Proceedings of the Spanish Relativity
Meeting (ERE) 2010, Granada, Spai
An extension of the cosmological standard model with a bounded Hubble expansion rate
The possibility of having an extension of the cosmological standard model
with a Hubble expansion rate constrained to a finite interval is
considered. Two periods of accelerated expansion arise naturally when the
Hubble expansion rate approaches to the two limiting values. The new
description of the history of the universe is confronted with cosmological data
and with several theoretical ideas going beyond the standard cosmological
model.Comment: 10 pages, 4 figures. Minor revisio
String versus Einstein frame in an AdS/CFT induced quantum dilatonic brane-world universe
AdS/CFT induced quantum dilatonic brane-world where 4d boundary is flat or de
Sitter (inflationary) or Anti-de Sitter brane is considered. The classical
brane tension is fixed but boundary QFT produces the effective brane tension
via the account of corresponding conformal anomaly induced effective action.
This results in inducing of brane-worlds in accordance with AdS/CFT set-up as
warped compactification. The explicit, independent construction of quantum
induced dilatonic brane-worlds in two frames: string and Einstein one is done.
It is demonstrated their complete equivalency for all quantum cosmological
brane-worlds under discussion, including several examples of classical
brane-world black holes. This is different from quantum corrected 4d dilatonic
gravity where de Sitter solution exists in Einstein but not in Jordan (string)
frame. The role of quantum corrections on massive graviton perturbations around
Anti-de Sitter brane is briefly discussed.Comment: LaTeX file, 24 pages, minor changes to match with published versio
Study of stop and sbottom at LHC
In supersymmetric models a gluino can decay into
through a stop or a sbottom. The decay chain produces an edge structure in the
distribution. Monte Carlo simulation studies show that the end point
and the edge height would be measured at the CERN LHC by using a sideband
subtraction technique. The stop and sbottom masses as well as their decay
branching ratios are constrained by the measurement. We study interpretations
of the measurement.Comment: 3 pages, 2 eps files, style files are included, talk at PASCOS'03,
Mumbai, India, January 3-8, 200
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
Unifying inflation with dark energy in modified F(R) Horava-Lifshitz gravity
We study FRW cosmology for a non-linear modified F(R) Horava-Lifshitz gravity
which has a viable convenient counterpart. A unified description of early-time
inflation and late-time acceleration is possible in this theory, but the
cosmological dynamic details are generically different from the ones of the
convenient viable F(R) model. Remarkably, for some specific choice of
parameters they do coincide. The emergence of finite-time future singularities
is investigated in detail. It is shown that these singularities can be cured by
adding an extra, higher-derivative term, which turns out to be qualitatively
different when compared with the corresponding one of the convenient F(R)
theory.Comment: LaTeX 12 pages, typos are correcte
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
- …