Inflatonless inflation

Whichever turns out to be the real theory of gravitation, the corresponding low-energy effective Lagrangian will probably contain higher derivative terms. In this work we study the general conditions on those terms in order to produce enough inflation to solve some of the problems of the standard Friedmann-Robertson-Walker cosmology in the absence of any inflaton field. We apply our results to some particular scenarios where higher derivative terms appear in the effective Lagrangian for gravity, such as those coming from graviton (two) loops or integrating out ordinary mater (such as the one present in the standard model).