Some Anisotropic Universes in the Presence of Imperfect Fluid Coupling with Spatial Curvature

Abstract

We consider Bianchi VI spacetime, which also can be reduced to Bianchi types VI 0 -V-III-I. We initially consider the most general form of the energy-momentum tensor which yields anisotropic stress and heat flow. We then derive an energy-momentum tensor that couples with the spatial curvature in a way so as to cancel out the terms that arise due to the spatial curvature in the evolution equations of the Einstein field equations. We obtain exact solutions for the universes indefinitely expanding with constant mean deceleration parameter. The solutions are beriefly discussed for each Bianchi type. The dynamics of the models and fluid are examined briefly, and the models that can approach to isotropy are determined. We conclude that even if the observed universe is almost isotropic, this does not necessarily imply the isotropy of the fluid (e.g., dark energy) affecting the evolution of the universe within the context of general relativity.

Accelerating dark energy models of the universe in anisotropic Bianchi type space-times and recent observations

“…For the value of ω to be in consistent with observa tion (Knop et al [50]), we have the following general condition for n ≠ 0 (72) where (73) and (74) For this constrain, the EoS parameter ω is restricted to the limit -1.67 < ω < -0.62 which is exactly in good agreement with the limit obtained from observational results coming from SN Ia data (Knop et al [50]). For the value of ω to be in consistent with observa tion (Tegmark et al [10]), we have the following gen eral condition for n ≠ 0 (75) where (76) and (77) For this constrain we obtain -1.33 < ω < -0.79 which is in good agreement with the limit obtained from observational results coming from SNe Ia data with CMB anisotropy and galaxy clustering statistics (Teg mark et al [10]).…”

“…This ansatz generalized the one proposed by Amirhashchi et al [83]. In litera ture it is common to use a constant deceleration parameter [73,74,85,90]. The motivation to choose such time dependent DP is behind the fact that the universe is accelerated expansion at present as observed in recent observations of Type Ia supernova [1][2][3][4][5][6] and CMB anisotropies [7][8][9] and decelerated expansion in the past.…”

“…The energy conservation equation of the perfect fluid gives (140) where as energy conservation equation of the DE component leads to (141) Following, Akarsu and Kilinc [73,74], Yadav [54] and Kumar and Yadav [90], we assume that the EoS parameter of the perfect fluid to be constant, that is,…”

“…Setare [64][65][66] and Setare and Saridakis [67][68][69] have also studied the DE models in different contexts. Recently, dark energy models with variable EoS parameter have been studied by Ray et al [70], Akarsu and Kilinc [71][72][73][74], Yadav et al [75], Yadav and Yadav [76], Yadav and Saha [77] Pradhan and Amirhashchi [78,79], Pradhan et al [80][81][82], Amirhashchi et al [83][84][85][86], Kumar [87,88], Kumar and Akarsu [89], Kumar and Yadav [90] and Kumar and Singh [91]. In well known reviews on modified gravity [92,93], it is clearly indicated that any modified gravity may be represented as effective fluid with time dependent ω.…”

Bianchi Type- I Bulk Viscosity with a DE Cosmological Model

“…Different scholars investigated models in the backdrop of general relativity within different Bianchi forms. For type-I Bianchi, DE models using constant deceleration parameter have been investigated by Akarsu and Kilinc [44,45]. Yadav et al [46] constructed Bianchi type-I DE cosmological models with the deceleration parameter with a variable of EoS parameter.…”