New agegraphic dark energy model in Brans-Dicke theory with logarithmic form of scalar field

Abstract

Recently, the current authors (arXiv:gr-qc/1609.01477) have proposed and analyzed in detail the logarithmic form of Brans-Dicke scalar field φ as φ ∝ ln(α+βa), where α and β are positive constants, to alleviate the problems of interacting holographic dark energy models in Brans-Dicke theory. In this paper, the cosmological evolution of a new agegraphic dark energy (NADE) model within the framework of Friedmann-Robertson-Walker Universe is analyzed with the same form of scalar field in Brans-Dicke theory. We derive the equation of state parameter w D and deceleration parameter q of NADE model. It is observed that w D → −1 when a → ∞, i.e., the NADE mimics cosmological constant in the late time evolution. Indeed, due to the assumption of logarithmic form of Brans-Dicke scalar field the NADE in Brans-Dicke theory behaves like NADE in general relativity in the late time evolution. The NADE model shows a phase transition from matter dominated phase in early time to accelerated phase in late time. We further extend NADE model by including the interaction between dark matter and NADE. In this case, w D definitely crosses the phantom divide line (w D = −1) in the late time evolution. The phase transition from matter dominated to NADE dominated phase may be achieved at early stage in interacting model. Further, we show that the interacting NADE model resolves the cosmic coincidence problem as the energy density ratio may evolve sufficiently slow at present.

Evolution of Density Parameters on a Smooth Embedded Universe

“…The matter density parameter is denoted by m (z) = 0 m (1 + z) 3 , r ad (z) = 0 r ad (1 + z) 4 and the term ext (z) = 0 ext (1 + z) 4−2β 0 e ±γ (z) stands for the density parameter associated with the extrinsic curvature. The upper script "0" indicates the present value of a quantity.…”

“…For any cosmological model it is important to reproduce at least the observed evolution of density parameters which consist in one of the important keys to understand the formation, dynamics and destiny of the universe. [1][2][3][4][5][6][7] In this paper we follow this direction to study the modification imposed on Friedman's equation when the standard model of the universe is regarded as an embedded space-time. As shown in previous works, [8] the contribution of the extrinsic curvature to the gravitational equations may play a fundamental role in replacing the phenomenological X-matter model.…”

A new holographic dark energy model in Brans-Dicke theory with logarithmic scalar field

“…The Hubble radius L = H −1 plays the role of the system's IR cutoff. Following [5], we have taken a logarithmic BD scalar field which gives a dynamical DP. Then we evaluated and plotted the density parameter, EoS and DP in terms of redshift.…”

“…As in [5], we assume a logarithmic relation between BD scalar field and scale factor which is claimed that it may avoid a constant result for the deceleration parameter:…”

“…To do this, we will choose a logarithmic form for the BD scalar field [5] which its aim is to check better agreement with observations and for the energy density of HDE we will take the form which have been proposed in [6]. In the presented model, we deal with the recent accelerated expansion and some other problems associated with the DE models like cosmic coincidence problem in a flat FRW geometry.…”