A Time-DependentΛandGCosmological Model Consistent with Cosmological Constraints

Abstract

The prevailing constantΛ-Gcosmological model agrees with observational evidence including the observed red shift, Big Bang Nucleosynthesis (BBN), and the current rate of acceleration. It assumes that matter contributes 27% to the current density of the universe, with the rest (73%) coming from dark energy represented by the Einstein cosmological parameterΛin the governing Friedmann-Robertson-Walker equations, derived from Einstein’s equations of general relativity. However, the principal problem is the extremely small value of the cosmological parameter (~10−52 m2). Moreover, the dark energy density represented byΛis presumed to have remained unchanged as the universe expanded by 26 orders of magnitude. Attempts to overcome this deficiency often invoke a variableΛ-Gmodel. Cosmic constraints from action principles require that either bothGandΛremain time-invariant or both vary in time. Here, we propose a variableΛ-Gcosmological model consistent with the latest red shift data, the current acceleration rate, and BBN, provided the split between matter and dark energy is 18% and 82%.Λdecreases (Λ~τ-2, whereτis the normalized cosmic time) andGincreases (G~τn) with cosmic time. The model results depend only on the chosen value ofΛat present and in the far future and not directly onG.

Bianchi Type-II Fractional Cosmological Model with Variable Lambda

“…In order to solve the Einstein field equations, they assumed that the cosmological term Λ was proportional to R −m where m being a constant and R represents the scale factor. Similarly time-dependent gravitational and cosmological constants investigated by several researchers [11], [18], [20], [23], [27], [33] and [34]. Bianchi Type space -times was also studied by so many authors assuming different conditions [2], [3], [8], [17], [22], [25] and [28].…”

Cosmology with variable $G$ and nonlinear electrodynamics

“…In Einstein's field equation, G acts as a coupling constant between the geometry of spacetime and matter. In quantum mechanics, G is essential in the definition of the Planck constant [52]. While in SCM, G is an invariant quantity.…”

Cosmology with Variable <em>G</em> and Nonlinear Electrodynamics

“…In the Einstein's field equation, G acts as a coupling constant between geometry of spacetime and matter. In quantum mechanics, G is essential in the definition of Planck constant [48]. While in SCM, G is an invariant quantity, it has been noted that there are significant evidence that gravitational constant G can be varying in a time [49].…”