Primordial and late-time inflation in Brans-Dicke cosmology

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 BransDicke theory of gravity. We show that the ratio of these two inflation parameters is proportional to the square root of the Brans-Dicke parameter ω (ω ≫ 1). 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 H . Bog̃aziçi Univ., Dept. of Physics, Bebek, Istanbul, Turkey E-mail: [email protected], [email protected]