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 arenot 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 upto the fourth derivative of the scale factor). when we consider the case of a radiation-filled universe, it turns out thatthe effects of these new terms cancel if we adhere to the robertson-walker mertic (which has built into it the observedfeatures of homogeneity and isotropy). we find r(t)=b√t(1+l t^p) and r(t)=b√t 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 muchsmaller 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.