Power law Starobinsky model of inflation from no-scale SUGRA

We consider a power law 1M2Rβ 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 β=2β=2 can change the value of tensor-to-scalar ratio from r∼O(10−3)r∼O(10−3) to r∼O(0.1)r∼O(0.1). We find that in order to get large tensor perturbation r≈0.1r≈0.1 as indicated by BKP measurements, we require the value of β≈1.83β≈1.83 thereby breaking global Weyl symmetry. We show that the general RβRβ model can be obtained from a SUGRA construction by adding a power law (Φ+Φ¯)n term to the minimal no-scale SUGRA Kähler potential. We further show that this two-parameter power law generalization of the Starobinsky model is equivalent to generalized non-minimal curvature coupled models of the form ξϕaRb+λϕ4(1+γ)ξϕaRb+λϕ4(1+γ) and thus the power law Starobinsky model is the most economical parametrization of such models.