LRS Bianchi Type – I Magnetized Anisotropic Dark Energy Models with Variable Equation of State

We discuss two dark energy models on LRS Bianchi Type-I magnetized anisotropic space –time with a variable equation of state (EoS). The EoS for dark energy  is found to be time dependent and its existing range for derive models is in good agreement with the recent observations. Using the suitable condition, the anisotropic models approach to isotropic scenario. We also find that during the evolution of the universe, the EoS parameter for DE changes from 1    to 1    in first model whereas from 1    to 1    in second model which is consistent with recent observations. The cosmological constant  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 supernovae Ia observations. The physical and geometric properties are also discussed. © 2017 Elixir All rights reserved. Elixir Space Sci. 103 (2017) 45758-45767 Space Science Available online at www.elixirpublishers. com (Elixir International Journal) Amrapali P. Wasnik et al./ Elixir Space Sci. 103 (2017) 45758-45767 45759 luminosity distances of high redshift type Ia supernovae and galaxy clustering, constrain the dark energy EoS to 92 . 0 44 . 1      at 68% confidence level [34,35], However, it is not at all obligatory to use a constant value of  . Due to lack of the observational evidence in making a distinction between constant and variable  , usually the equation of state parameter is considered as a constant [36,37,4] with phase wise value 1 , 3 1 , 0 , 1    and for vacuum fluid, dust fluid, radiation and stiff dominated universe respectively. But in general,  is a function of time or redshift [38,39,40]. Some literature are also available on models with varying fields, such as cosmological models with variable EoS parameter in Kaluza-Klein metric and wormhole [41,42]. In recent years various form of time dependent  have been used for variable  models by Mukhopadhyay et al. [43]. In well –known reviews on modified gravity [44,45],it is clearly indicated that any modified gravity may be represented as effective fluid with time dependent  . In Principle, once the metric is generalized to Bianchi types, the EoS parameter of the fluid can be generalized in a way conveniently to wield anisotropy with the considered metric . In such model, where both the metric and EoS parameter of the fluid are allowed to exhibit an anisotropic character, the universe can exhibit non-trivial isotropization histories and it can be examined whether the metric and/or the EoS parameter of fluid evolve toward isotropy. We may say about two main classes of such models; according to whether this anisotropization occurs at an early time or at late times of the universe, The former class can be related with the inflation field , which drives the inflation, which drives the late time acceleration of the universe. In the context of the former class, the generic inflationary model can be modified in a way to end inflation with a slightly anisotropic spatial geometry. Bianchi type-I universe is the prime candidate for studying the possible effects of an anisotropy in the early universe on presentday observations, there are few other models (for example, 0 VI B  ), which describe an anisotropic space-time and generate interest among physicists. [46-49]. Pradhan and Bali [50] and Bali et al. [51] have studied 0 VI B  space time in connection with massive strings. Recently Amirhashchi et al.[52] presented dark energy models in an anisotropic 0 VI B  space –time by considering constant deceleration parameter. In this paper, we have investigated two new LRS Bianchi type-I magnetized dark energy models with variable equation of state . The discussion of the paper is as follows: In section.2, the metric and the field equations are described. In section 3 deals with the solutions of the field equations in two different cases . Section 4 deals with physical and geometric behavior of the models. In section 5, we describe an other dark energy model and its physical aspects. Finally, conclusions are summarized in the last Section 6. 2. Metric and Field Equations: We consider the LRS Bianchi Type-I metric in the following form ) ( 2 2 2 2 2 2 2 dz dy b dx a dt ds      (1) where the scale factors a and b are functions of cosmic time only. The energy momentum tensor for anisotropic dark energy with magnetic field is given by i j EM i j DE i j T T T   (2) where i j j i ED ED i j DE pg u u p T    ) ( (3) where i u is the flow vector satisfying 1   j i ij u u g (4) i j EM T is the electromagnetic field tensor which is given by               F F g g F F T ij j i ij EM