Accidental inflation from Kähler uplifting

We analyze the possibility of realizing inflation with a subsequent dS vacuum in the Käahler uplifting scenario. The inclusion of several quantum corrections to the 4d effective action evades previous no-go theorems and allows for construction of simple and successful models of string inflation. The predictions of several benchmark models are in accord with current observations, i.e., a red spectral index, negligible non-gaussianity, and spectral distortions similar to the simplest models of inflation. A particularly interesting subclass of models are ``left-rolling" ones, where the overall volume of the compactified dimensions shrinks during inflation. We call this phenomenon ``inflation by deflation" (IBD), where deflation refers to the internal manifold. This subclass has the appealing features of being insensitive to initial conditions, avoiding the overshooting problem, and allowing for observable running α ∼ 0.012 and enhanced tensor-to-scalar ratio r ∼ 10−5. The latter results differ significantly from many string inflation models

R2 log R quantum corrections and the inflationary observables

We study a model of inflation with terms quadratic and logarithmic in the Ricci scalar, where the gravitational action is f(R)=R+α R2+β R2 ln R. These terms are expected to arise from one loop corrections involving matter fields in curved space-time. The spectral index ns and the tensor to scalar ratio yield 4 × 10-4≲ r≲0.03 and 0.94≲ ns ≲ 0.99. i.e. r is an order of magnitude bigger or smaller than the original Starobinsky model which predicted r∼ 10-3. Further enhancement of r gives a scale invariant ns∼ 1 or higher. Other inflationary observables are d ns/dln k ≳ -5.2 × 10-4, μ ≲ 2.1 × 10-8 , y ≲ 2.6 × 10-9. Despite the enhancement in r, if the recent BICEP2 measurement stands, this model is disfavoured