Brans-Dicke cosmology,II

We discuss the implications of the Brans-Dicke scalar-tensor theory for cosmology with particular emphasis on the primordial element abundances that would obtain. Two general classes of models are found. Models of one class expand through the nuclear burning stage slightly more rapidly than the general relativistic case: models of the other class may expand at any rate whatsoever. The first class of models yeilds primordial abundances of D, He³ and He⁴ in agreement with their general relativistic values if the present mass density is low. High-density cosmologies, however, would produce too much He⁴. The second class of models yields element abundances which are far too high unless the expansion rate was quite large: in this case no He⁴ at all is produced. Finally, we determine the rate of change of the constant of gravitationG at the present epoch. For all but a very small class of models is negative at the present epoch. Models with positive values of at the present epoch produce no primordial He⁴ whatsoever, and have ages significantly lower than the corresponding general relativistic ages.