Initial conditions for Starobinsky Inflation with a positive spatial curvature

Abstract

We have found numerically initial conditions in the $(R, H)$ plane leading to a successful Starobinsky inflation in $R+R^2$ gravity for a isotropic metrics with positive spatial curvature. Trajectories can reach inflation regime either directly or going through a bounce, and even recollapse followed by a bounce. Our numerical plots indicate that ``good" initial conditions exist even for big initial spatial curvature, however, we argue that such a trajectory must cross a region of rather big $R$ or $H$. This means that the range of viability of $R+R^2$ theory in the $(R,H)$ plane directly affect the question of viability of Starobinsky inflation for a positive spatial curvature isotropic Universe.