6,105 research outputs found
Transition from quintessence to phantom phase in quintom model
Assuming the Hubble parameter is a continuous and differentiable function of
comoving time, we investigate necessary conditions for quintessence to phantom
phase transition in quintom model. For power-law and exponential potential
examples, we study the behavior of dynamical dark energy fields and Hubble
parameter near the transition time, and show that the phantom-divide-line w=-1
is crossed in these models.Comment: LaTeX, 19 pages, four figures, some minor changes in Introduction,
two figures added and the references updated, accepted for publication in
Phys. Rev.
Thermodynamical description of the interacting new agegraphic dark energy
We describe the thermodynamical interpretation of the interaction between new
agegraphic dark energy and dark matter in a non-flat universe. When new
agegraphic dark energy and dark matter evolve separately, each of them remains
in thermodynamic equilibrium. As soon as an interaction between them is taken
into account, their thermodynamical interpretation changes by a stable thermal
fluctuation. We obtain a relation between the interaction term of the dark
components and this thermal fluctuation.Comment: 11 pages, accepted for publication in MPLA (2010
Unification of Dark Matter and Dark Energy in a Modified Entropic Force Model
In Verlinde's entropic force scenario of gravity, Newton's laws and Einstein
equations can be obtained from the first pinciples and general assumptions.
However, the equipartition law of energy is invalid at very low temperatures.
We show clearly that the threshold of the equipartition law of energy is
related with horizon of the universe. Thus, a one-dimension Debye (ODD) model
in the direction of radius of the modified entropic force (MEF) maybe suitable
in description of the accelerated expanding universe. We present a Friedmann
cosmic dynamical model in the ODD-MEF framework. We examine carefully
constraints on the ODD-MEF model from the Union2 compilation of the Supernova
Cosmology Project (SCP) collaboration, the data from the observation of the
large-scale structure (LSS) and the cosmic microwave background (CMB), i.e. SNe
Ia+LSS+CMB. The combined numerical analysis gives the best-fit value of the
model parameters and , with
. The corresponding age of the universe agrees with the
result of D. Spergel {\it et al.}\cite{Spergel2003} at 95% confidence level.
The numerical result also yields an accelerated expanding universe without
invoking any kind of dark energy. Taking as a
running parameter associated with the structure scale , we obtain a possible
unified scenario of the asymptotic flatness of the radial velocity dispersion
of spiral galaxies, the accelerated expanding universe and the Pioneer 10/11
anomaly in the entropic force framework of Verlinde.Comment: 23 pages, 6 figure
Thermodynamics of interacting entropy-corrected holographic dark energy in a non-flat FRW universe
A so-called "entropy-corrected holographic dark energy" (ECHDE), was recently
proposed to explain the dark energy-dominated universe with the help of quantum
corrections to the entropy-area relation in the setup of loop quantum
cosmology. Using this new definition, we investigate its thermodynamical
features including entropy and energy conservation. We describe the
thermodynamical interpretation of the interaction between ECHDE and dark matter
in a non-flat universe. We obtain a relation between the interaction term of
the dark components and thermal fluctuation. Our study further generalizes the
earlier works [M.R. Setare and E.C. Vagenas, Phys. Lett. B 666 (2008) 111; B.
Wang et al., Phys. Lett. B 662 (2008) 1] in this direction.Comment: 14 pages, no figure, accepted by Int. J. Mod. Phys.
Renormalization of tensor-network states
We have discussed the tensor-network representation of classical statistical
or interacting quantum lattice models, and given a comprehensive introduction
to the numerical methods we recently proposed for studying the tensor-network
states/models in two dimensions. A second renormalization scheme is introduced
to take into account the environment contribution in the calculation of the
partition function of classical tensor network models or the expectation values
of quantum tensor network states. It improves significantly the accuracy of the
coarse grained tensor renormalization group method. In the study of the quantum
tensor-network states, we point out that the renormalization effect of the
environment can be efficiently and accurately described by the bond vector.
This, combined with the imaginary time evolution of the wavefunction, provides
an accurate projection method to determine the tensor-network wavfunction. It
reduces significantly the truncation error and enable a tensor-network state
with a large bond dimension, which is difficult to be accessed by other
methods, to be accurately determined.Comment: 18 pages 23 figures, minor changes, references adde
Crossing w=-1 in Gauss-Bonnet Brane World with Induced Gravity
Recent type Ia supernovas data seemingly favor a dark energy model whose
equation of state crosses -1 very recently, which is a much more amazing
problem than the acceleration of the universe. In this paper we show that it is
possible to realize such a crossing without introducing any phantom component
in a Gauss-Bonnet brane world with induced gravity, where a four dimensional
curvature scalar on the brane and a five dimensional Gauss-Bonnet term in the
bulk are present. In this realization, the Gauss-Bonnet term and the mass
parameter in the bulk play a crucial role.Comment: Revtex 16 pages including 10 eps files, references added, to appear
in Comm. Theor. Phy
Comparison of dark energy models: A perspective from the latest observational data
In this paper, we compare some popular dark energy models under the
assumption of a flat universe by using the latest observational data including
the type Ia supernovae Constitution compilation, the baryon acoustic
oscillation measurement from the Sloan Digital Sky Survey, the cosmic microwave
background measurement given by the seven-year Wilkinson Microwave Anisotropy
Probe observations and the determination of from the Hubble Space
Telescope. Model comparison statistics such as the Bayesian and Akaike
information criteria are applied to assess the worth of the models. These
statistics favor models that give a good fit with fewer parameters. Based on
this analysis, we find that the simplest cosmological constant model that has
only one free parameter is still preferred by the current data. For other
dynamical dark energy models, we find that some of them, such as the
dark energy, constant , generalized Chaplygin gas,
Chevalliear-Polarski-Linder parametrization, and holographic dark energy
models, can provide good fits to the current data, and three of them, namely,
the Ricci dark energy, agegraphic dark energy, and Dvali-Gabadadze-Porrati
models, are clearly disfavored by the data.Comment: 19 pages, 10 figures; new data used, typos fixed; version for
publication in SCIENCE CHINA Physics, Mechanics & Astronom
Cosmological Evolution of Hessence Dark Energy and Avoidance of the Big Rip
Recently, many dark energy models whose equation-of-state parameter can cross
the phantom divide have been proposed. In a previous paper [Class.
Quant. Grav. {\bf 22}, 3189 (2005); hep-th/0501160], we suggest such a model
named hessence, in which a non-canonical complex scalar field plays the role of
dark energy. In this work, the cosmological evolution of the hessence dark
energy is investigated. We consider two cases: one is the hessnece field with
an exponential potential, and the other is with a (inverse) power law
potential. We separately investigate the dynamical system with four different
interaction forms between hessence and background perfect fluid. It is found
that the big rip never appears in the hessence model, even in the most general
case, beyond particular potentials and interaction forms.Comment: 15 pages, 8 tables, revtex4; v2: references added; v3: published
versio
Geometrothermodynamics of the Kehagias-Sfetsos Black Hole
The application of information geometric ideas to statistical mechanics using
a metric on the space of states, pioneered by Ruppeiner and Weinhold, has
proved to be a useful alternative approach to characterizing phase transitions.
Some puzzling anomalies become apparent, however, when these methods are
applied to the study of black hole thermodynamics. A possible resolution was
suggested by Quevedo et al. who emphasized the importance of Legendre
invariance in thermodynamic metrics. They found physically consistent results
for various black holes when using a Legendre invariant metric, which agreed
with a direct determination of the properties of phase transitions from the
specific heat.
Recently, information geometric methods have been employed by Wei et al. to
study the Kehagias-Sfetsos (KS) black hole in Horava-Lifshitz gravity. The
formalism suggests that a coupling parameter in this theory plays a role
analogous to the charge in Reissner-Nordstrom (RN) black holes or angular
momentum in the Kerr black hole and calculation of the specific heat shows a
singularity which may be interpreted as a phase transition. When the curvature
of the Ruppeiner metric is calculated for such a theory it does not, however,
show a singularity at the phase transition point.
We show that the curvature of a particular Legendre invariant ("Quevedo")
metric for the KS black hole is singular at the phase transition point. We
contrast the results for the Ruppeiner, Weinhold and Quevedo metrics and in the
latter case investigate the consistency of taking either the entropy or mass as
the thermodynamic potential.Comment: v2: some references adde
- …