Vol 13, No 2 (2013) / Pradhan

Accelerating dark energy models with anisotropic fluid in Bianchi type VI0 space-time

Anirudh Pradhan

Abstract

Motivated by the increasing evidence for the need of a geometry that resembles Bianchi morphology to explain the observed anisotropy in the WMAP data, we have discussed some features of Bianchi type VI0 universes in the presence of a fluid that has an anisotropic equation of state (EoS) parameter in general relativity. We present two accelerating dark energy (DE) models with an anisotropic fluid in Bianchi type VI0 space-time. To ensure a deterministic solution, we choose the scale factor a(t) = sqrt{t^n e^t} , which yields a time-dependent deceleration parameter, representing a class of models which generate a transition of the universe from the early decelerating phase to the recent accelerating phase. Under suitable conditions, the anisotropic models approach an isotropic scenario. The EoS for DE ω is found to be time-dependent and its existing range for derived models is in good agreement with data from recent observations of type Ia supernovae (SNe Ia) (Knop et al. 2003), SNe Ia data combined with cosmic microwave background (CMB) anisotropy and galaxy clustering statistics (Tegmark et al. 2004a), as well as the latest combination of cosmological datasets coming from CMB anisotropies, luminosity distances of high redshift SNe Ia and galaxy clustering. For different values of n, we can generate a class of physically viable DE models. The cosmological constant Λ is found to be a positive decreasing function of time and it approaches a small positive value at late time (i.e. the present epoch), which is corroborated by results from recent SN Ia observations. We also observe that our solutions are stable. The physical and geometric aspects of both models are also discussed in detail.

Keywords


cosmological models — dark energy — variable EoS parameter

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