Abstract
From a LagrangianL= (1/κ)(-g)1/2[R/2+l2(αR ik R ik+βR 2)] one obtains fourth-order field equations for the metrical tensorg ik. Inserting a 3-flat Robertson-Walker line element, the set of their vacuum solutions will be enumerated completely. The qualitative behavior, and especially the influence of thel 2-terms (which is possibly necessary for the renormalization of quantum gravity) in certain stages of evolution follow from a phase plane analysis. Depending on the sign of coupling, one obtains either exponentially increasing or oscillating solutions at late times as well as special solutions without an initial singularity.
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