Inflationary attractors in F(R) gravity

In this letter we shall demonstrate that the viable F(R)gravities can be classified mainly into two classes of inflationary attractors, either the R^2attractors or the \alphaattractors. To show this, we shall derive the most general relation between the tensor-to-scalar ratio rand the spectral index of primordial curvature perturbations n_s namely the r-n_srelation, by assuming that the slow-roll condition constrains the values...