Coasting cosmologies with time dependent cosmological constant

TL;DR

This paper explores coasting cosmological models with a time-dependent cosmological constant within scalar-tensor theories, showing they feature linear expansion and a decreasing gravitational constant, aligning with Dirac's hypothesis.

Contribution

It introduces coasting cosmologies with a variable cosmological constant and gravitational constant, providing solutions consistent with Dirac's hypothesis in scalar-tensor frameworks.

Findings

Linear expansion in coasting cosmologies

Gravitational constant decreases inversely with time

Cosmological constant decreases inversely with square of time

Abstract

The effect of a time dependent cosmological constant is considered in a family of scalar tensor theories. Friedmann-Robertson-Walker cosmological models for vacumm and perfect fluid matter are found. They have a linear expansion factor, the so called coasting cosmology, the gravitational "constant" decreace inversely with time; this model satisfy the Dirac hipotesis. The cosmological "constant" decreace inversely with the square of time, therefore we can have a very small value for it at present time.