Power law Starobinsky model of inflation from no-scale SUGRA

We consider a power law 1/(MR beta)-R-2 correction to Einstein gravity as a model for inflation. The interesting feature of this form of generalization is that small deviations from the Starobinsky limit beta = 2 can change the value of tensor-to-scalarratio from r similar to O(10(-3)) to r similar to O(0.1). We find that in order to get large tensor perturbation r approximate to 0.1 as indicated by BKP measurements, we require the value of beta approximate to 1.83 thereby breaking global Weyl symmetry. We show that the general R-beta model can be obtained from a SUGRA construction by adding a power law (Phi + (Phi) over bar)(n) term to the minimal no-scale SUGRA Kahler potential. We further show that this two-parameterpower law generalization of the Starobinsky model is equivalent to generalized non-minimal curvature coupled models of the form xi phi R-a(b)+lambda phi(4(1+gamma)) and thus the power law Starobinsky model is the most economical parametrization of such models. (C) 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license.