Quintom Dark Energy Model Research Articles

String inspired quintom model with non-minimally coupled modified gravity

In this Letter we consider a quintom model of dark energy with non-minimal coupling between scalar field and modified gravity which is known f(R) gravity. The Lagrangian for scalar field has been inspired by tachyonic Lagrangian in string theory. Then we obtain the equation of state (EoS), and the condition required for the model parameters when ω crosses over −1. This model shows that for having ω across over −1, one doesn't need to add some higher derivative operator in the tachyonic part of action (the way that usually used to obtain crossing of the phantom divide line for EoS parameter).

Quintom dark energy models with nearly flat potentials

We examine quintom dark energy models, produced by the combined consideration of a canonical and a phantom field, with nearly flat potentials and dark energy equation-of-state parameter $w_{DE}$ close to -1. We find that all such models converge to a single expression for $w_{DE}(z)$, depending only on the initial field values and their derivatives. We show that this quintom paradigm allows for a description of the transition through -1 in the near cosmological past. In addition, we provide the necessary conditions for the determination of the direction of the -1-crossing.

PROBING FOR THE COSMOLOGICAL PARAMETERS WITH PLANCK MEASUREMENT

In this paper we investigate the constraints on the cosmological parameters, especially the equation of state of dynamical dark energy w DE , the inflationary parameters ns, αs and r, the total neutrino mass ∑ mν and the curvature of the universe ΩK, using the simulated data of future Planck measurement. First, we determine the cosmological parameters with the current observations, including ESSENCE (192 samples), Three-Year WMAP (WMAP3), Boomerang-2K2, CBI, VSA, ACBAR, SDSS LRG and 2dFGRS, and then we take the best-fit model as the fiducial model in the ensuing simulations. In the simulations we pay particular attention to the effects of the dynamical dark energy in the determination of the cosmological parameters. For this reason, in order to make our constraints more robust, we have added the simulated SNAP data to our simulations. Using the present data, we find that the Quintom dark energy model is mildly favored, while the ΛCDM model remains a good fit. In the framework of the dynamical dark energy model, the constraints on the inflationary parameters, ∑ mν and ΩK, become weak, compared with the constraints in the ΛCDM model. Intriguingly, we find that the inflationary models with a "blue" tilt, which are excluded about 2σ in the ΛCDM model, are well within the 2σ region with the presence of the dynamics of dark energy. The upper limits of neutrino mass are weakened by a factor of 2 (95% CL) — say, ∑ mν < 1.59 eV and ∑ mν < 1.53 eV for two forms of parametrization of the equation of state of dark energy. The flat universe is a good fit to the current data, namely |ΩK| < 0.03 (95% CL). With the simulated Planck and SNAP data, the dynamical dark energy model and the ΛCDM model might be distinguished at the 4σ confidence level. And the uncertainties of the inflationary parameters, ∑ mν and ΩK, can be reduced significantly in the framework of the dynamical dark energy model. We also constrain the rotation angle Δα, denoting the possible CPT violation, from the simulated Planck and CMBpol data and find that our results are much more stringent than the current constraint and will be used to verify the CPT symmetry with a higher precision.

Reconstructing a string-inspired quintom model of dark energy

In this Letter, we develop a simple method for the reconstruction of the string-inspired dark energy model with the Lagrangian L=−V(ϕ)1−α′∇μϕ∇μϕ+β′ϕ□ϕ given by Cai et al., which may allow the equation-of-state parameter cross the cosmological constant boundary (w=−1). We reconstruct this model in the light of three forms of parametrization for dynamical dark energy.

The quintom model with O(N) symmetry

We investigate the quintom model of dark energy in the generalizedcase where the corresponding canonical and phantom fields possessO(N) symmetries. Assuming exponential potentials we find that thisO(N) quintom paradigm exhibits novel properties comparing to the simple canonical and phantomscenarios. In particular, we find that the universe cannot result in a quintessence-type solution withw>−1, even in the cases where the phantom field seems to be irrelevant. On the contrary, thereare always late-time attractors which correspond to accelerating universes withw<−1 and with a recent crossing of the phantom divide, and for a very large area of theparameter space they are the only ones. This is in contrast with the previous simplequintom results, where an accelerating universe is a possible late-time stable solution but itis not guaranteed.

First-Order Formalism for the Quintom Model of Dark Energy

The present paper deals to the quintom model of dark energy. We introduce a first-order formalism, which shows how to relate the potential that specifies the scalar field model to Hubble’s parameter. Reviewing briefly the quintom scenario of dark energy, we present a general procedure to solve the equations of motion for quintom model driven by a couple scalar fields with first-order differential equations.

Non-minimally coupled quintom model inspired by string theory

In this Letter we consider a quintom model of dark energy with a single scalar field T given by a Lagrangian which inspired by tachyonic Lagrangian in string theory. We consider non-minimal coupling of tachyon field to the scalar curvature, then we obtain the equation of state (EoS), and the condition required for the model parameters when ω crosses over −1.

A string-inspired quintom model of dark energy

We propose in this Letter a quintom model of dark energy with a single scalar field ϕ given by the Lagrangian L = − V ( ϕ ) ( 1 − α ′ ∇ μ ϕ ∇ μ ϕ + β ′ ϕ □ ϕ ) 1 / 2 . In the limit of β ′ → 0 our model reduces to the effective low energy Lagrangian of tachyon considered in the literature. We study the cosmological evolution of this model, and show explicitly the behaviors of the equation of state crossing the cosmological constant boundary.

Avoiding the big-rip jeopardy in a quintom dark energy model with higher derivatives

In the framework of a single scalar field quintom model with higher derivative, we construct in this paper a dark energy model of which the equation of state (EOS) $w$ crosses over the cosmological constant boundary. Interestingly during the evolution of the universe $w<-1$ happens just for a period of time with a distinguished feature that $w$ starts with a value above -1, transits into $w<-1$, then comes back to $w>-1$. This avoids the Big Rip jeopardy induced by $w<-1$.

Generalized second law of thermodynamics in quintom dominated universe

In this paper we will investigate the validity of the Generalized Second Law of thermodynamics for the Quintom model of dark energy. Reviewing briefly the quintom scenario of dark energy, we will study the conditions of validity of the generalized second law of thermodynamics in three cases: quintessence dominated, phantom dominated and transition from quintessence to phantom will be discussed.

Development of the Model of the Generalized Quintom DarkEnergy

We consider a generalized quintom (GQ) dark energy model for changingthe equal weight of the negative-kinetic scalar field (phantom) and thenormal scalar field (quintessence) in quintom dark energy. Though thephantom-dominated scaling solution is a stable late-time attractor, theearly evolution of GQ is different from that of the quintom model andthe adjustability of the dark energy state equation in the model isimproved.

Perturbations of the quintom models of dark energy and the effects on observations

We study in this paper the perturbations of the quintom dark energy model and the effects of quintom perturbations on the current observations. Quintom describes a scenario of dark energy where the equation of state gets across the cosmological constant boundary $w=\ensuremath{-}1$ during evolution. We present a new method to show that the conventional dark energy models based on a single $k$-essence field and perfect fluid cannot act as the quintom due to the singularities and classical instabilities of perturbations around $w=\ensuremath{-}1$. One needs to add extra degrees of freedom for successful quintom model building. There are no singularities or classical instabilities in perturbations of realistic quintom models and they are potentially distinguishable from the cosmological constant. Basing on the realistic quintom models in this paper we provide one way to include the perturbations for dark energy models with parametrized equation of state across $\ensuremath{-}1$. Compared with those assuming no dark energy perturbations, we find that the parameter space which allows the equation of state to get across $\ensuremath{-}1$ will be enlarged, in general, when including the perturbations.

CONSTRAINTS ON OSCILLATING QUINTOM FROM SUPERNOVA, MICROWAVE BACKGROUND AND GALAXY CLUSTERING

We consider in this paper a simple oscillating Quintom model of dark energy which has two free parameters and an equation of state oscillating and crossing -1. For low redshifts the equation of state of this model resembles itself similar to the linearly parametrized dark energy, however differs substantially at large redshifts. We fit our model to the observational data separately from the new high redshifts supernova observations from the HST/GOODS program and previous supernova, CMB and galaxy clustering. Our results show that because of the oscillating feature of our model the constraints from observations at large redshifts such as CMB become less stringent.

Hessence: a new view of quintom dark energy

Recently a lot of attention has been given to building a dark energy model in which the equation-of-state parameter w can cross the phantom divide w = −1. One of the models to realize crossing the phantom divide is called the quintom model, in which two real scalar fields appear, 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-ball 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.

Cosmological evolution of a quintom model of dark energy

We investigate in this Letter the cosmological evolution of a dark energy model with two scalar fields where one of the scalar has canonical kinetic energy and another scalar has negative kinetic energy term. For such a system with exponential potentials we find that during the evolution of the universe the equation of state w changes from w⩾−1 to w<−1, which is consistent with the recent observations. A phase-plane analysis shows that the “phantom”-dominated scaling solution is the stable late-time attractor of this type of models.