5,108 research outputs found

### Non-Abelian gauge fields in the gradient expansion: generalized Boltzmann and Eilenberger equations

We present a microscopic derivation of the generalized Boltzmann and
Eilenberger equations in the presence of non-Abelian gauges, for the case of a
non-relativistic disordered Fermi gas. A unified and symmetric treatment of the
charge $[U(1)]$ and spin $[SU(2)]$ degrees of freedom is achieved. Within this
framework, just as the $U(1)$ Lorentz force generates the Hall effect, so does
its $SU(2)$ counterpart give rise to the spin Hall effect. Considering elastic
and spin-independent disorder we obtain diffusion equations for charge and spin
densities and show how the interplay between an in-plane magnetic field and a
time dependent Rashba term generates in-plane charge currents.Comment: 11 pages, 1 figure; some corrections and updated/extended reference

### Scalar models for the generalized Chaplygin gas and the structure formation constraints

The generalized Chaplygin gas model represents an attempt to unify dark
matter and dark energy. It is characterized by a fluid with an equation of
state $p = - A/\rho^\alpha$. It can be obtained from a generalization of the
DBI action for a scalar, tachyonic field. At background level, this model gives
very good results, but it suffers from many drawbacks at perturbative level. We
show that, while for background analysis it is possible to consider any value
for $\alpha$, the perturbative analysis must be restricted to positive values
of $\alpha$. This restriction can be circumvented if the origin of the
generalized Chaplygin gas is traced back to a self-interacting scalar field,
instead of the DBI action. But, in doing so, the predictions coming from
formation of large scale structures reduce the generalized Chaplygin gas model
to a kind of quintessence model, and the unification scenario is lost, if the
scalar field is the canonical one. However, if the unification condition is
imposed from the beginning as a prior, the model may remain competitive. More
interesting results, concerning the unification program, are obtained if a
non-canonical self-interacting scalar field, inspired by Rastall's theory of
gravity, is imposed. In this case, an agreement with the background tests is
possible.Comment: Latex file, 25 pages, 33 figures in eps format. New section on scalar
models. Accepted for publication in Gravitation&Cosmolog

### Statefinder Parameters for Five-Dimensional Cosmology

We study the statefinder parameter in the five-dimensional big bounce model,
and apply it to differentiate the attractor solutions of quintessence and
phantom field. It is found that the evolving trajectories of these two
attractor solutions in the statefinder parameters plane are quite different,
and that are different from the statefinder trajectories of other dark energy
models.Comment: 8 pages, 12 figures. accepted by MPL

### Holographic Dark Energy Scenario and Variable Modified Chaplygin Gas

In this letter, we have considered that the universe is filled with normal
matter and variable modified Chaplygin gas. Also we have considered the
interaction between normal matter and variable modified Chaplygin gas in FRW
universe. Then we have considered a correspondence between the holographic dark
energy density and interacting variable modified Chaplygin gas energy density.
Then we have reconstructed the potential of the scalar field which describes
the variable modified Chaplygin cosmology.Comment: 4 latex pages, no figures, RevTeX styl

### Conservation laws and scattering for de Sitter classical particles

Starting from an intrinsic geometric characterization of de Sitter timelike
and lightlike geodesics we give a new description of the conserved quantities
associated with classical free particles on the de Sitter manifold. These
quantities allow for a natural discussion of classical pointlike scattering and
decay processes. We also provide an intrinsic definition of energy of a
classical de Sitter particle and discuss its different expressions in various
local coordinate systems and their relations with earlier definitions found in
the literature.Comment: 25 pages, 1 figur

### Interacting Ricci Dark Energy and its Statefinder Description

In this paper we have considered an interacting Ricci dark energy in flat FRW
universe. We have reconstructed the Hubble's parameter under this interaction.
Also, we have investigated the statefinder diagnostics. It has been revealed
that the equation of state parameter behaves like quintessence in this
interaction and from the statefinder diagnostics it has been concluded that the
interacting Ricci dark energy interpolates between dust and $\Lambda$CDM stages
of the universe.Comment: 9 pages, 3 figure

### Positive Quantum Brownian Evolution

Using the independent oscillator model with an arbitrary system potential, we
derive a quantum Brownian equation assuming a correlated total initial state.
Although not of Lindblad form, the equation preserves positivity of the density
operator on a restricted set of initial states

### Statefinder diagnostic for holographic dark energy model

In this paper we study the holographic dark energy model proposed by Li from
the statefinder viewpoint. We plot the evolutionary trajectories of the model
with $c=1$ in the statefinder parameter-planes. The statefinder diagrams
characterize the properties of the holographic dark energy and show the
discrimination between this scenario and other dark energy models. We also
perform a statefinder diagnostic to the holographic dark energy model in cases
of different $c$ which given by three fits to observational data. The result
indicates that from the statefinder viewpoint $c$ plays a significant role in
this model and should thus be determined seriously by future high precision
experiments.Comment: 13 pages, 3 figure

### Iso-spectral potential and inflationary quantum cosmology

Using the factorization approach of quantum mechanics, we obtain a family of
isospectral scalar potentials for power law inflationary cosmology. The
construction is based on a scattering Wheeler-DeWitt solution. These
iso-spectrals have new features, they give a mechanism to end inflation, as
well as the possibility to have new inflationary epochs. The procedure can be
extended to other cosmological models.Comment: 14 pages, 5 figure

### Can the Chaplygin gas be a plausible model for dark energy?

In this note two cosmological models representing the flat Friedmann Universe
filled with a Chaplygin fluid, with or without dust, are analyzed in terms of
the recently proposed "statefinder" parameters. Trajectories of both models in
the parameter plane are shown to be significantly different w.r.t. "quiessence"
and "tracker" models. The generalized Chaplygin gas model with an equation of
state of the form $p = -A/\rho^{\alpha}$ is also analyzed in terms of the
statefinder parameters.Comment: 6 pages, 2 figure

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