Single-field inflation in models with an $R^2$ term

Abstract

We present two cases where the addition of the $R^2$ term to an inflationary model leads to single-field inflation instead of two-field inflation as is usually the case. In both cases we find that the effect of the $R^2$ term is to reduce the value of the tensor-to-scalar ratio $r$.

Comments: 18 pages, 7 figures, invited talk given at Corfu Summer Institute 2019 "School and Workshops on Elementary Particle Physics and Gravity", 31 August - 25 September 2019, Corfu, Greece