107 research outputs found
Cosmic Duality in Quintom Universe
In this paper we study the duality in two-field Quintom models of Dark Energy. We find that an expanding universe dominated by Quintom-A field is dual to a contracting universe with Quintom-B field
Inflationary universe in loop quantum cosmology
Loop quantum cosmology provides a nice solution of avoiding the big bang
singularity through a big bounce mechanism in the high energy region. In loop
quantum cosmology an inflationary universe is emergent after the big bounce, no
matter what matter component is filled in the universe. A super-inflation phase
without phantom matter will appear in a certain way in the initial stage after
the bounce; then the universe will undergo a normal inflation stage. We discuss
the condition of inflation in detail in this framework. Also, for slow-roll
inflation, we expect the imprint from the effects of the loop quantum cosmology
should be left in the primordial perturbation power spectrum. However, we show
that this imprint is too weak to be observed.Comment: 21 pages, 4 figures; accepted for publication in JCA
Natural Phantom Dark Energy, Wiggling Hubble Parameter and Direct Data
Recent direct data indicate that the parameter may wiggle with
respect to . On the other hand the luminosity distance data of supernovae
flatten the wiggles of because of integration effect. It is expected
that the fitting results can be very different in a model permitting a wiggling
because the data of supernovae is highly degenerated to such a model. As
an example the natural phantom dark energy is investigated in this paper. The
dynamical property of this model is studied. The model is fitted by the direct
data set and the SNLS data set, respectively. And the results are quite
different, as expected. The quantum stability of this model is also shortly
discussed. We find it is a viable model if we treat it as an effective theory
truncated by an upperbound.Comment: 14 pages, 2 figures, discussions on the stability added, conclusions
not change
Hessence: A New View of Quintom Dark Energy
Recently a lot of attention has been drawn to build dark energy model in
which the equation-of-state parameter can cross the phantom divide .
One of models to realize crossing the phantom divide is called quintom model,
in which two real scalar fields appears, one is a normal scalar field and the
other is a phantom-type scalar field. In this paper we propose a non-canonical
complex scalar field as the dark energy, which we dub ``hessence'', to
implement crossing the phantom divide, in a similar sense as the quintom dark
energy model. In the hessence model, the dark energy is described by a single
field with an internal degree of freedom rather than two independent real
scalar fields. However, the hessence is different from an ordinary complex
scalar field, we show that the hessence can avoid the difficulty of the Q-balls
formation which gives trouble to the spintessence model (An ordinary complex
scalar field acts as the dark energy). Furthermore, we find that, by choosing a
proper potential, the hessence could correspond to a Chaplygin gas at late
times.Comment: Latex2e, 12 pages, no figure; v2: discussions and references added,
14 pages, 3 eps figures; v3: published versio
Cosmological evolution of interacting phantom (quintessence) model in Loop Quantum Gravity
The dynamics of interacting dark energy model in loop quantum cosmology (LQC)
is studied in this paper. The dark energy has a constant equation of state
and interacts with dark matter through a form . We
find for quintessence model () the cosmological evolution in LQC is the
same as that in classical Einstein cosmology; whereas for phantom dark energy
(), although there are the same critical points in LQC and classical
Einstein cosmology, loop quantum effect reduces significantly the parameter
spacetime () required by stability. If parameters and satisfy
the conditions that the critical points are existent and stable, the universe
will enter an era dominated by dark energy and dark matter with a constant
energy ratio between them, and accelerate forever; otherwise it will enter an
oscillatory regime. Comparing our results with the observations we find at
confidence level the universe will accelerate forever.Comment: 15 pages, 8 figures, to appear in JCA
Cosmological Evolution of Interacting Phantom Energy with Dark Matter
We investigate the cosmological evolution of an interacting phantom energy
model in which the phantom field has interaction with the dark matter. We
discuss the existence and stability of scaling solutions for two types of
specific interactions. One is motivated by the conformal transformation in
string theory and the other is motivated by analogy with dissipation. In the
former case, there exist no scaling solutions. In the latter case, there exist
stable scaling solutions, which may give a phenomenological solution of the
coincidence problem. Furthermore, the universe either accelerates forever or
ends with a singularity, which is determined by not only the model parameters
but also the initial velocity of the phantom field.Comment: 7 pages, 11 figures, RevTe
Dark Energy Model with Spinor Matter and Its Quintom Scenario
A class of dynamical dark energy models, dubbed Spinor Quintom, can be
constructed by a spinor field with a nontraditional potential. We find
that, if choosing suitable potential, this model is able to allow the
equation-of-state to cross the cosmological constant boundary without
introducing any ghost fields. In a further investigation, we show that this
model is able to mimic a perfect fluid of Chaplygin gas with during
the evolution, and also realizes the Quintom scenario with its
equation-of-state across -1.Comment: 20 pages, 5 figures, accepted by CQG, several references adde
Super-acceleration on the Brane by Energy Flow from the Bulk
We consider a brane cosmological model with energy exchange between brane and
bulk. Parameterizing the energy exchange term by the scale factor and Hubble
parameter, we are able to exactly solve the modified Friedmann equation on the
brane. In this model, the equation of state for the effective dark energy has a
transition behavior changing from to , while
the equation of state for the dark energy on the brane has . Fitting data
from type Ia supernova, Sloan Digital Sky Survey and Wilkinson Microwave
Anisotropy Probe, our universe is predicted now in the state of
super-acceleration with .Comment: Revtex, 11 pages including 2 figures,v2: tpos fixed, references
added, to appear in JCA
UV stable, Lorentz-violating dark energy with transient phantom era
Phantom fields with negative kinetic energy are often plagued by the vacuum
quantum instability in the ultraviolet region. We present a Lorentz-violating
dark energy model free from this problem and show that the crossing of the
cosmological constant boundary w=-1 to the phantom equation of state is
realized before reaching a de Sitter attractor. Another interesting feature is
a peculiar time-dependence of the effective Newton's constant; the magnitude of
this effect is naturally small but may be close to experimental limits. We also
derive momentum scales of instabilities at which tachyons or ghosts appear in
the infrared region around the present Hubble scale and clarify the conditions
under which tachyonic instabilities do not spoil homogeneity of the
present/future Universe.Comment: 22 pages, 7 figures; Presentation modified substantially, results and
conclusions unchanged. Journal versio
- …