Cosmology withG and Λ coupling scalars

A Mathematical Aspect of FRW - Cosmological Models Varying t and Λ

“…Therefore, it is thought that the real solutions of Einstein's field equations cannot be stationary. As discussed earlier by many researchers [4,5] that a constant ( ) Λ cannot explain the huge difference between the cosmological constant inferred from observations and energy density resulting from quantum field theories. The cosmological constant ( ) Λ was introduced such that it was large in the early universe and then decayed with evolution.…”

“…Beesham [10] studied a universe consisting of a cosmological constant (Λ ∼ ) and bulk viscosity. More recently Abdel Rahman considered a model in which the gravitational constant G varies with time but energy is conserved [5,6,9]. In the present work will investigate the effects of viscosity in a universe vary with…”

“…A number of models with different decay laws for the variation of cosmological term were investigated during last two decades by Abdel-Rahaman 1990 [6] and Berman 1991 [2], Maharaj and Naido 1993 [7] who obtained cosmological model with time dependent G and Λ terms, and suggested that Λ ∼ . Many authors [1,3,5,6] have proposed linking of the variation of G with that of Λ within the rules of general relativity. Mathematically well-posed gravitation theories were developed in which Einstein's theory of general relativity was generalized to include a varying Λ by deriving it from Friedmann equation satisfying a conservation equation.…”

“…Mathematically well-posed gravitation theories were developed in which Einstein's theory of general relativity was generalized to include a varying Λ by deriving it from Friedmann equation satisfying a conservation equation. There has been considerable interest in solutions of Einstein's equations of early universe both from cosmological as well as mathematical point of view [1,5,6,7].…”

Scenarios of Cosmic String With a Variable Cosmological Constant

“…Λ = Λ(t)) as well as astrophysical situations (i.e. Λ = Λ(r)) by several workers 15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30 . Now, string theory being a major tool for understanding nature involving physical systems a string theoretic approach towards astrophysical and cosmological realm thought to be useful from the very beginning of the advent of the theory.…”