Present Age Of Universe Research Articles

LRS Bianchi Type II Massive String Cosmological Model for Stiff Fluid Distribution with Decaying Vacuum Energy (Λ)

An LRS Bianchi Type II model formed by massive strings with decaying vacuum energy (Λ) for stiff fluid distribution is studied in the context of general relativity. To get the deterministic model, we have assumed that \(\frac{\sigma}{\theta} =\mathrm{constant}\) where σ is shear and θ the expansion in the model and decaying vacuum energy (Λ) is proportional to H2 (H is Hubble parameter) as used in Arbab (Gen. Relativ. Gravit. 29:51, 1997). We find that the model represents decelerating and accelerating phases of universe. The decaying vacuum energy (Λ) is proportional to \(\frac{1}{\tau^{2}}\) as obtained by Bertolami (Nuovo Cimento B 93:36, 1986) and Hubble parameter is proportional to \(\frac{1}{\tau}\) which matches with the observation. The model in general represents anisotropic space-time. However, in special case, it isotropizes. The particle density (ρp) and string tenson (λ) are initially large but decrease due to lapse of time. The model also admits particle horizon and entropy is inversely proportional absolute temperature. Thus the model is in good agreement with present age of universe.

Cosmology with non-linear scalar field

Mukhanov and Vikman have studied inflation model with the non-linear (NL) scalar field. We discuss the dark energy model with the Lagrangian in the presence of the square potential. We analyse the sufficient condition for the existence of an attractor solution, and compare the equation of state parameter, the present age of universe and the transition redshift with the quintessence model. We also use the Gold dataset of 157 SN-Ia to finally constrain the parameter of the models. We find that the considered model is consistent with the observation and a little inferior to the quintessence model. The above Lagrangian is similar to the non-linear Born–Infeld (NLBI) scalar field model, while which is superior to the quintessence model.

A COMPARISON OF QUINTESSENCE AND NON-LINEAR BORN–INFELD SCALAR FIELD USING GOLD SUPERNOVA DATA

We study the Non-Linear Born–Infeld (NLBI) scalar field model and quintessence model with two different potentials (V(ϕ) = -sϕ and [Formula: see text]). We investigate the differences between these two models. We explore the equation of state parameter w and the evolution of scale factor a(t) in both the NLBI scalar field and quintessence model. The present age of universe and the transition redshift are also obtained. We use the Gold dataset of 157 SN-Ia to constrain the parameters of the two models. All the results show that the NLBI model is slightly superior to the quintessence model.