The Imaginary Starobinsky Model and Higher Curvature Corrections
  We elaborate on the predictions of the imaginary Starobinsky model of inflation coupled to matter, where the inflaton is identified with the imaginary part of the inflaton multiplet suggested by the Supergravity embedding of a pure R + R^2 gravity. In particular, we study the impact of higher-order curvature terms and show that, depending on the parameter range, one may find either a quadratic model of chaotic inflation or monomial models of chaotic inflation with fractional powers between 1 and 2. 
Sergio Ferrara, Alex Kehagias and Antonio Riotto
hep-th astro-ph.CO gr-qc hep-ph