Generalized inflation from R³ and R□R terms

Generalized inflationary stages as power‐law solutions result from the addition of R 3 and R □ R terms to the quadratic gravitational Lagrangian. Both contributions lead to new attractor solutions in the high‐curvature limit. We emphasize the properties of critical values of the curvature scalar in the R 3 theory. Contrarily to models with two scalar fields, the higher order curvature terms allow double inflation for special initial conditions only.