Primordial and late-time inflation in Brans-Dicke cosmology

Abstract

The basic motivation of this work is to attempt to explain the rapid primordial inflation and the observed slow late-time inflation by using the Brans-Dicke theory of gravity. We show that the ratio of primordial and late-time inflation parameters is proportional to the square root of the Brans-Dicke parameter w(). We also calculate the Hubble parameter H and the time variation of the time dependent Newtonian gravitational constant G for both regimes. The variation of the Hubble parameter predicted by Brans-Dicke cosmology is shown to be consistent with recent measurements: The value of H in the late-time future is predicted as 0.86 times the present value of H0. By using a linearized non-vacuum late time solution in Brans-Dicke cosmology we account for the seventy five percent dark energy contribution but not for approximately twenty-three percent dark matter contribution to the present day energy density of the universe. In the context of Brans-Dicke scalar tensor theory of gravitation, the cosmological Friedmann Equation which relates the expansion rate H of the universe to the various fractions of energy density is analyzed rigorously. And it is shown that Brans-Dicke scalar tensor theory of gravitation brings a negligible correction to the power of the scale size term in the matter density component of Friedmann equation. In addition to 歔 and M in standard Einstein cosmology, another density parameter, ¢, is expected by the theory. This implies that if ¢ is found to be nonzero, data will favor this model instead of the standard Einstein cosmological model with cosmological constant and will enable more accurate predictions for the rate of change of Newtonian gravitational constant in the future.