Quintom dark energy in DGP braneworld cosmology

In this paper we consider a $Z_2$ symmetrical 3-brane embedded in a 5-dimensional spacetime. We study the effective Einstein equation and acceleration condition in presence of the quintom dark energy fluid as the bulk matter field. It is shown that the time-dependent bulk quintom field induces a time-dependent cosmological constant on the brane. In the framework of the DGP model, the effective Einstein equation is obtained in two different cases: i) where the quintom field is considered as the bulk matter field and the brane is empty and, ii) where the quintom dark energy is confined on the brane and the bulk is empty. We show that in both cases one could obtain a self-inflationary solution at late time in positive branch $\epsilon=1$, and an asymptotically static universe in negative branch $\epsilon=-1$.Comment: 12 pages, 8 figure

Holographic Chaplygin gas model

In this paper we consider a correspondence between the holographic dark energy density and Chaplygin gas energy density in FRW universe. Then we reconstruct the potential and the dynamics of the scalar field which describe the Chaplygin cosmology.Comment: 9 pages, no figure

Interacting holographic dark energy model in non-flat universe

We employ the holographic model of interacting dark energy to obtain the equation of state for the holographic energy density in non-flat (closed) universe enclosed by the event horizon measured from the sphere of horizon named $L$.Comment: 8 pages, the address of author changed, some references adde

The holographic dark energy in non-flat Brans-Dicke cosmology

In this paper we study cosmological application of holographic dark energy density in the Brans-Dicke framework. We employ the holographic model of dark energy to obtain the equation of state for the holographic energy density in non-flat (closed) universe enclosed by the event horizon measured from the sphere of horizon named $L$. Our calculation show, taking $\Omega_{\Lambda}=0.73$ for the present time, the lower bound of $w_{\rm \Lambda}$ is -0.9. Therefore it is impossible to have $w_{\rm \Lambda}$ crossing -1. This implies that one can not generate phantom-like equation of state from a holographic dark energy model in non-flat universe in the Brans-Dicke cosmology framework. In the other hand, we suggest a correspondence between the holographic dark energy scenario in flat universe and the phantom dark energy model in framework of Brans-Dicke theory with potential.Comment: 10 pages, no figures, abstract and text extended, references adde

Interacting holographic generalized Chaplygin gas model

In this paper we consider a correspondence between the holographic dark energy density and interacting generalized Chaplygin gas energy density in FRW universe. Then we reconstruct the potential of the scalar field which describe the generalized Chaplygin cosmology.Comment: 12 pages, no figur

String or M theory axion as a quintessence

A slow-rolling scalar field ($Q\equiv$ Quintessence) with potential energy $V_Q\sim (3\times 10^{-3} {\rm eV})^4$ has been proposed as the origin of accelerating universe at present. We investigate the effective potential of $Q$ in the framework of supergravity model including the quantum corrections induced by generic (nonrenormalizable) couplings of $Q$ to the gauge and charged matter multiplets. It is argued that the K\"ahler potential, superpotential and gauge kinetic functions of the underlying supergravity model are required to be invariant under the variation of $Q$ with an extremely fine accuracy in order to provide a working quintessence potential. Applying these results for string or $M$-theory, we point out that the heterotic $M$-theory or Type I string axion can be a plausible candidate for quintessence if (i) it does not couple to the instanton number of gauge interactions not weaker than those of the standard model and (ii) the modulus partner ${\rm Re}(Z)$ of the periodic quintessence axion ${\rm Im}(Z)\equiv {\rm Im}(Z)+1$ has a large VEV: ${\rm Re}(Z)\sim \frac{1}{2\pi}\ln(m_{3/2}^2 M_{Planck}^2/V_Q)$. It is stressed that such a large ${\rm Re}(Z)$ gives the gauge unification scale at around the phenomenologically favored value $3\times 10^{16}$ GeV. To provide an accelerating universe, the quintessence axion should be at near the top of its effective potential at present, which requires a severe fine tuning of the initial condition of $Q$ and $\dot{Q}$ in the early universe. We discuss a late time inflation scenario based on the modular and CP invariance of the moduli effective potential, yielding the required initial condition in a natural manner if the K\"ahler metric of the quintessence axion superfield receives a sizable nonperturbative contribution.Comment: 23 pages, 3 figures, version to be published at Phys. Rev.