101 research outputs found
Effective Finite Temperature Partition Function for Fields on Non-Commutative Flat Manifolds
The first quantum correction to the finite temperature partition function for
a self-interacting massless scalar field on a dimensional flat manifold
with non-commutative extra dimensions is evaluated by means of dimensional
regularization, suplemented with zeta-function techniques. It is found that the
zeta function associated with the effective one-loop operator may be nonregular
at the origin. The important issue of the determination of the regularized
vacuum energy, namely the first quantum correction to the energy in such case
is discussed.Comment: amslatex, 14 pages, to appear in Phys. Rev.
Casimir energy-momentum tensor for a brane in de Sitter spacetime
Vacuum expectation values of the energy-momentum tensor for a conformally
coupled scalar field is investigated in de Sitter (dS) spacetime in presence of
a curved brane on which the field obeys the Robin boundary condition with
coordinate dependent coefficients. To generate the corresponding vacuum
densities we use the conformal relation between dS and Rindler spacetimes and
the results previously obtained by one of the authors for the Rindler
counterpart. The resulting energy-momentum tensor is non-diagonal and induces
anisotropic vacuum stresses. The asymptotic behaviour of this tensor is
investigated near the dS horizon and the boundary.Comment: 10 pages, no figur
Interacting Dark Energy in Ho\v{r}ava-Lifshitz Cosmology
In the usual Ho\v{r}ava-Lifshitz cosmological models, the scalar field is
responsible for dark matter. Using an additional scalar field, Saridakis
\cite{sari} has formulated Ho\v{r}ava-Lifshitz cosmology with an effective dark
energy sector. In the paper \cite{sari} the scalar fields do not interact with
each other, here we extend this work to the interacting case, where matter
scalar field interact with dark energy scalar field . We will
show that in contrast with \cite{sari}, where -filed is absent, we can
obtain , that is we result to an effective dark energy
presenting phantom behaviour. This behaviour is pure effect of the interaction.Comment: 10 pages, no figur
Interacting Three Fluid System and Thermodynamics of the Universe Bounded by the Event Horizon
The work deals with the thermodynamics of the universe bounded by the event
horizon. The matter in the universe has three constituents namely dark energy,
dark matter and radiation in nature and interaction between then is assumed.
The variation of entropy of the surface of the horizon is obtained from unified
first law while matter entropy variation is calculated from the Gibbss' law.
Finally, validity of the generalized second law of thermodynamics is examined
and conclusions are written point wise.Comment: 7 page
Interacting new agegraphic Phantom model of dark energy in non-flat universe
In this paper we consider the new agegraphic model of interacting dark energy
in non-flat universe. We show that the interacting agegraphic dark energy can
be described by a phantom scalar field. Then we show this phantomic description
of the agegraphic dark energy and reconstruct the potential of the phantom
scalar field.Comment: 8 pages, no figur
Phantom phase power-law solution in gravity
Power-law solutions for gravity coupled with perfect fluid have been
studied for spatially flat universe. It is shown that despite the matter
dominated and accelerating power-law solutions, the power-law solution exists
for an special form of when this universe enters a Phantom phase.Comment: 10 pages, Published online in Astrophysics and Space Scienc
Multiple CDM cosmology with string landscape features and future singularities
Multiple CDM cosmology is studied in a way that is formally a
classical analog of the Casimir effect. Such cosmology corresponds to a
time-dependent dark fluid model or, alternatively, to its scalar field
presentation, and it motivated by the string landscape picture. The future
evolution of the several dark energy models constructed within the scheme is
carefully investigated. It turns out to be almost always possible to choose the
parameters in the models so that they match the most recent and accurate
astronomical values. To this end, several universes are presented which mimick
(multiple) CDM cosmology but exhibit Little Rip, asymptotically de
Sitter, or Type I, II, III, and IV finite-time singularity behavior in the far
future, with disintegration of all bound objects in the cases of Big Rip,
Little Rip and Pseudo-Rip cosmologies.Comment: LaTeX 11 pages, 10 figure
Crack propagation and fracture in silicon wafers under thermal stress
The behaviour of microcracks in silicon during thermal annealing has been studied using in situ X-ray diffraction imaging. Initial cracks are produced with an indenter at the edge of a conventional Si wafer, which was heated under temperature gradients to produce thermal stress. At temperatures where Si is still in the brittle regime, the strain may accumulate if a microcrack is pinned. If a critical value is exceeded either a new or a longer crack will be formed, which results with high probability in wafer breakage. The strain reduces most efficiently by forming (hhl) or (hkl) crack planes of high energy instead of the expected low-energy cleavage planes like {111}. Dangerous cracks, which become active during heat treatment and may shatter the whole wafer, can be identified from diffraction images simply by measuring the geometrical dimensions of the strain-related contrast around the crack tip. Once the plastic regime at higher temperature is reached, strain is reduced by generating dislocation loops and slip bands and no wafer breakage occurs. There is only a small temperature window within which crack propagation is possible during rapid annealing
Dark energy from conformal symmetry breaking
The breakdown of conformal symmetry in a conformally invariant scalar-tensor
gravitational model is revisited in the cosmological context. Although the old
scenario of conformal symmetry breaking in cosmology containing scalar field
has already been used in many earlier works, it seems that no special attention
has been paid for the investigation on the possible connection between the
breakdown of conformal symmetry and the existence of dark energy. In this
paper, it is shown that the old scenario of conformal symmetry breaking in
cosmology, if properly interpreted, not only has a potential ability to
describe the origin of dark energy as a symmetry breaking effect, but also may
resolve the coincidence problem.Comment: 11 pages, minor revision, published online in EPJ
Holographic dark energy with time varying parameter
We consider the holographic dark energy model in which the model parameter
evolves slowly with time. First we calculate the evolution of EoS
parameter as well as the deceleration parameter in this generalized version of
holographic dark energy (GHDE). Depending on the parameter , the phantom
regime can be achieved earlier or later compare with original version of
holographic dark energy. The evolution of energy density of GHDE model is
investigated in terms of parameter . We also show that the time-dependency
of can effect on the transition epoch from decelerated phase to
accelerated expansion. Finally, we perform the statefinder diagnostic for GHDE
model and show that the evolutionary trajectories of the model in plane
are strongly depend on the parameter .Comment: 16 pages, 4 figures, accepted by Astrophys Space Sc
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