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I briefly review the observational evidence for a small cosmological constant at the present epoch. This evidence mainly comes from high redshift observations of Type 1a supernovae, which, when combined with CMB observations strongly support a flat Universe with Ωm + ΩA ⋍ 1. Theoretically a cosmological constant can arise from zero point vacuum fluctuations. In addition ultra-light scalar fields...
There is some consensus emerging on the values of the basic parameters of classical cosmology. The baryon number density estimated from the light element abundance or X-ray gas in galaxy clusters tends towards 5% of closure density; the dark matter content based on a number of independent methods appears to be somewhat less than half the closure density; Hubble constant obtained from local measurements,...
I start by defining the cosmological parameters H0, Θm and ΘA. Then I show how the age of the universe depends on them, followed by the evolution of the scale parameter of the universe for various values of the density parameters. Then I define strategies for measuring them, and show the results for the recent determination of these parameters from measurements on supernovas of type 1a. Implications...
I present a short overview of current observational results and theoretical models for a cosmological constant. The main motivation for invoking a small cosmological constant (or A-term) at the present epoch has to do with observations of high redshift Type Ia supernovae which suggest an accelerating universe. A flat accelerating universe is strongly favoured by combining supernovae observations with...
This talk presents a brief overview of recent results pertaining to the cosmological constant ‘A’. I summarize the observational situation focussing on observations of high redshift Type Ia supernovae which suggest A > 0. Observations of small angular anisotropies in the cosmic microwave background complement Type Ia supernovae observations and both CMB and Sn can be combined to place strong constraints...
The paper aims to introduce a new symmetry principle in the space-time geometry through the elimination of the classical idea of rest and by including a universal minimum speed limit in the subatomic world. Such a limit, unattainable by particles, represents the preferred reference frame associated with a universal background field that breaks Lorentz symmetry. Thus, the structure of space-time is...
Had Einstein followed the Bianchi differential identity for the derivation of his equation of motion for gravitation, Λ would have emerged as a true new constant of spacetime on the same footing as the velocity of light? It is then conceivable that he could have perhaps made the most profound prediction that the Universe may suffer accelerated expansion some time in the future! Further we argue that...
We investigate the role played by the cosmological constant during gravitational collapse of a radiating star with vanishing Weyl stresses in the interior. We highlight the role played by the cosmological constant during the latter stages of collapse. The evolution of the temperature of the collapsing body is studied by employing causal heat transport equation. We show that the inclusion of the cosmological...
The general class of Bianchi cosmological models with dark energy in the form of modified Chaplygin gas with variable Λ and G and bulk viscosity have been considered. We discuss three types of average scale factor by using a special law for deceleration parameter which is linear in time with negative slope. The exact solutions to the corresponding field equations are obtained. We obtain the solution...
The general class of anisotropic Bianchi cosmological models in f(R, T) modified theories of gravity with Λ(T) has been considered. This paper deals with f(R, T) modified theories of gravity, where the gravitational Lagrangian is given by an arbitrary function of Ricci scalar R and the trace of the stress-energy tensor T has been investigated for a specific choice of f(R, T) = f1(R) + f2(T). The exact...
In this paper, we have studied the locally rotationally symmetric (LRS) Bianchi type-I cosmological model filled with a bulk viscous cosmological fluid in $$f(R)$$ f(R) gravity in the presence of time-varying gravitational and cosmological constant. We have used the power-law and intermediate scenario for scale factor to obtain the solution of the field equations. The evolution of temperature of...
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