LRS Bianchi I model with constant deceleration parameter

Abstract

An LRS Bianchi I model is considered with constant deceleration parameter, q = α − 1, where α ≥ 0 is a constant. The physical and kinematical behaviour of the models for α = 0 and α = 0 is studied in detail. The model with α = 0 describes late time acceleration, but eternal inflation demands a violation of the NEC and WEC. The acceleration is caused by phantom matter which approaches a cosmological constant at late times. The solutions with a scalar field also show that the model is compatible with a phantom field only. A comparison with the observational outcomes indicates that the universe has entered into the present accelerating phase in recent past somewhere between 0.2 z 0.5. The model obeys the "cosmic no hair conjecture". The models with 0 < α < 1 describe late time acceleration driven by quintessence dark energy. A violation of the NEC and WEC is required to accommodate the early inflationary epoch caused by phantom matter. The models with 1 < α < 3 describe decelerating phases which are usually occur in the presence of dust or radiation. These models are also found anisotropic at early times and attain isotropy at late times. The model for α = 3 represents a stiff matter era which also has shear at early stages and becomes shear free at late times, but it evolves with an insignificant ceaseless anisotropy. The models with α > 3 violate the DEC and the corresponding scalar field models have negative potential which is physically unrealistic.

Plane symmetric model in f(R, T) gravity

“…This happens due to the parameter λ of f (R, T ) = R + 2λT gravity. The geometrical behaviors in this case also remains the same as in GR [66]. It is to be noted that these solutions were not reported by Sahoo et al [64].…”

Plane symmetric model with constant deceleration parameter

“…Thus, all the results and discussion related to the physical behavior presented in Ref. [3] will be true in the present model also.…”

“…where H i (i = 1, 2, 3) represents the directional Hubble parameters in the directions x, y, z respectively. On comparing these geometrical parameters with the one in an LRS Bianchi I model [3], we see that only the directional expansion rates are interchanged, but all other parameters remain identical in both models. Hence, both models evolve similarly kinematically as well.…”

“…Many authors have solved Einstein's equations using (1)-( 4) in GR as well as in some of the others theories of gravity (see Ref. [3] and references therein for a complete list of earlier works). These works were carried out in homogenous and isotropic space-times.…”

“…However, in Ref. [3], at a cost of a violation of the NEC and the WEC, we have advocated that the model can explain late time cosmic acceleration or even eternal inflation. The motivation fo the arguments is the positivity of the energy density for a time…”