A cosmological exact solution of generalized Brans - Dicke theory with complex scalar field and its phenomenological implications

When the Brans-Dicke theory is formulated in terms of the Jordan scalar field phi, the amount of dark energy is related to the mass of this field. We investigate a solution which is relevant to the late universe. We show that if phi is taken to be a complex scalar field, then an exact solution to the vacuum equations requires that the Friedmann equation possesses both a constant term and one which is proportional to the inverse sixth power of the scale factor. Possible interpretations and phenomenological implications of this result are discussed