Brans-Dicke-type theories and avoidance of the cosmological singularity - art. no. 044042

We study flat Friedmann-Robertson-Walker cosmology in a Brans-Dicke-type th eory of gravitation with minimal coupling between the scalar field and the matter fields in the Einstein frame (general relativity with an extra scala r field) for arbitrary values of the Brans-Dicke parameter omega>-3/2. It i s shown that the cosmological singularity occurring in the Einstein frame f ormulation of this theory is removed in the Jordan frame in the range -3/2< omega less than or equal to-4/3. This result is interpreted in the light of a viewpoint asserting that both Jordan frame and Einstein frame formulatio ns of general relativity are physically equivalent. The implications of the obtained result for string theory are outlined.