Can hyperbolic phase of Brans-Dicke field account for dark matter and dark energy?

Abstract

The main purpose of this thesis is to explain the dark matter and dark energy contribution to standard Friedmann Equation which relates the expansion rate of the universe, H; to the various fractions of the present energy densities of the universe by using Brans-Dicke theory of gravity in late-time regime. Firstly, vacuum solutions of the field equations will be analyzed and it will be shown that there is some anomaly in explaining the dark matter issue if Brans-Dicke field Á is solely assumed to be complex. Then, for the next step, a hyperbolic phase of Brans-Dicke field Á is worked out in the field equations and hence the anomaly seen under the assumption of complex Brans-Dicke field Á has been disappeared automat- ically. Therefore, we showed that Brans-Dicke scalar tensor theory well accounts for dark matter and dark energy provided that the Brans-Dicke field Á is modified suitably.