Will modification of the Einstein field equations have cosmological implications?

The field equations of general relativity can be derived from a stationary action principle. But these equations are not unique; they may be modified by adding, for example, a second order curvature term to the gravitational action. The inclusion of one such a small corrective term leads to a set of equations with four new terms (which involve up to the fourth derivative of the scale factor). When we consider the case of a radiation-filled universe, it turns out that the effects of these new terms cancel if we adhere to the Robertson-Walker mertic (which has built into it the ob- served features of homogeneity and isotropy). We find ???? ???? ?1 ? ???? and ???? ???? to be equally valid solutions of the modified field equations (where R(t) is the scale factor and b and l are constants; l is very much smaller than b; p = _ 1). Only the first and second derivatives of R turn out to be non-vanishing. The Robertson- Walker cosmology survives our modifications even for times that are long compared with the Planck time.