20 research outputs found

### Variable Modified Chaplygin Gas and Accelerating Universe

In this letter, I have proposed a model of variable modified Chaplygin gas
and shown its role in accelerating phase of the universe. I have shown that the
equation of state of this model is valid from the radiation era to quiessence
model. The graphical representations of statefinder parameters characterize
different phase of evolution of the universe. All results presented in the
letter concerns the case $k=0$.Comment: 7 Latex pages, 5 figures, revtex styl

### 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

### Dynamics of Logamediate and Intermediate Scenarios in the Dark Energy Filled Universe

We have considered a model of two component mixture i.e., mixture of
Chaplygin gas and barotropic fluid with tachyonic field. In the case, when they
have no interaction then both of them retain their own properties. Let us
consider an energy flow between barotropic and tachyonic fluids. In both the
cases we find the exact solutions for the tachyonic field and the tachyonic
potential and show that the tachyonic potential follows the asymptotic
behavior. We have considered an interaction between these two fluids by
introducing a coupling term. Finally, we have considered a model of three
component mixture i.e., mixture of tachyonic field, Chaplygin gas and
barotropic fluid with or without interaction. The coupling functions decays
with time indicating a strong energy flow at the initial period and weak stable
interaction at later stage. To keep the observational support of recent
acceleration we have considered two particular forms (i) Logamediate Scenario
and (ii) Intermediate Scenario, of evolution of the Universe. We have examined
the natures of the recent developed statefinder parameters and slow-roll
parameters in both scenarios with and without interactions in whole evolution
of the universe.Comment: 28 pages, 20 figure

### Dilatonic Interpretation of the Quintessence?

We discuss the possibility that "quintessential effects", recently displayed
by large scale observations, may be consistently described in the context of
the low-energy string effective action, and we suggest a possible approach to
the problem of the cosmic coincidence based on the link between the strength of
the dilaton couplings and the cosmological state of our Universe.Comment: 6 pages, Revtex, four figures included using epsfig. To appear in
Phys. Rev.

### Observational Constraints of Modified Chaplygin Gas in Loop Quantum Cosmology

We have considered the FRW universe in loop quantum cosmology (LQC) model
filled with the dark matter (perfect fluid with negligible pressure) and the
modified Chaplygin gas (MCG) type dark energy. We present the Hubble parameter
in terms of the observable parameters $\Omega_{m0}$, $\Omega_{x0}$ and $H_{0}$
with the redshift $z$ and the other parameters like $A$, $B$, $C$ and $\alpha$.
From Stern data set (12 points), we have obtained the bounds of the arbitrary
parameters by minimizing the $\chi^{2}$ test. The best-fit values of the
parameters are obtained by 66%, 90% and 99% confidence levels. Next due to
joint analysis with BAO and CMB observations, we have also obtained the bounds
of the parameters ($B,C$) by fixing some other parameters $\alpha$ and $A$.
From the best fit of distance modulus $\mu(z)$ for our theoretical MCG model in
LQC, we concluded that our model is in agreement with the union2 sample data.Comment: 14 pages, 10 figures, Accepted in EPJC. arXiv admin note: text
overlap with arXiv:astro-ph/0311622 by other author

### Interaction between Tachyon and Hessence (or Hantom) dark energies

In this paper, we have considered that the universe is filled with tachyon,
hessence (or hantom) dark energies. Subsequently we have investigated the
interactions between tachyon and hessence (hantom) dark energies and calculated
the potentials considering the power law form of the scale factor. It has been
revealed that the tachyonic potential always decreases and hessence (or hantom)
potential increases with corresponding fields. Furthermore, we have considered
a correspondence between the hessence (or hantom) dark energy density and new
variable modified Chaplygin gas energy density. From this, we have found the
expressions of the arbitrary positive constants B0 and C of new variable
modified Chaplygin gas

### Expanding Universe: Thermodynamical Aspects From Different Models

The pivotal point of the paper is to discuss the behavior of temperature,
pressure, energy density as a function of volume along with determination of
caloric EoS from following two model: $w(z)=w_{0}+w_{1}\ln(1+z)$ & $w(z)=-1+\frac{(1+z)}{3}\frac{A_{1}+2A_{2}(1+z)}{A_{0}+2A_{1}(1+z)+A_{2}(1+z)^{2}}$.
The time scale of instability for this two models is discussed. In the paper we
then generalize our result and arrive at general expression for energy density
irrespective of the model. The thermodynamical stability for both of the model
and the general case is discussed from this viewpoint. We also arrive at a
condition on the limiting behavior of thermodynamic parameter to validate the
third law of thermodynamics and interpret the general mathematical expression
of integration constant $U_{0}$ (what we get while integrating energy
conservation equation) physically relating it to number of micro states. The
constraint on the allowed values of the parameters of the models is discussed
which ascertains stability of universe. The validity of thermodynamical laws
within apparent and event horizon is discussed.Comment: 16 pages, 3 figures(Accepted for publication in "Astrophysics and
Space Science"

### Bianchi Type V Viscous Fluid Cosmological Models in Presence of Decaying Vacuum Energy

Bianchi type V viscous fluid cosmological model for barotropic fluid
distribution with varying cosmological term $\Lambda$ is investigated. We have
examined a cosmological scenario proposing a variation law for Hubble parameter
$H$ in the background of homogeneous, anisotropic Bianchi type V space-time.
The model isotropizes asymptotically and the presence of shear viscosity
accelerates the isotropization. The model describes a unified expansion history
of the universe indicating initial decelerating expansion and late time
accelerating phase. Cosmological consequences of the model are also discussed.Comment: 10 pages, 3 figure

### Variable Modified Chaplygin Gas in Anisotropic Universe with Kaluza-Klein Metric

In this work, we have consider Kaluza-Klein Cosmology for anisotropic
universe where the universe is filled with variable modified chaplygin gas
(VMCG). Here we find normal scalar field $\phi$ and the self interacting
potential $V(\phi)$ to describe the VMCG Cosmology. Also we graphically
analyzed the geometrical parameters named {\it statefinder parameters} in
anisotropic Kaluza-Klein model. Next, we consider a Kaluza-Klein model of
interacting VMCG with dark matter in the Einstein gravity framework. Here we
construct the three dimensional autonomous dynamical system of equations for
this interacting model with the assumption that the dark energy and the dark
matter are interact between them and for that we also choose the interaction
term. We convert that interaction terms to its dimensionless form and perform
stability analysis and solve them numerically. We obtain a stable scaling
solution of the equations in Kaluza-Klein model and graphically represent
solutions.Comment: 11 pages, 13 figure

### Statefinder Description in Generalized Holographic and Ricci Dark Energy Models

We have considered the generalized holographic and generalized Ricci dark
energy models for acceleration of the universe. If the universe filled with
only GHDE/GRDE the corresponding decel- eration parameter, EOS parameter and
statefinder parameters have been calculated. Next we have considered that the
mixture of GHDE/GRDE and dark matter in interacting and non-interacting
situations. Also the mixture of GHDE/GRDE and generalized Chaplygin gas have
been analyzed during evolution of the universe. The natures of above mentioned
parameters have been investigated for interacting and non-interacting
situations. Finally, it follows that the prescribed models derive the
acceleration of the universe.Comment: 18 pages and 19 figure