Poly-instanton inflation

We propose a new inflationary scenario in type IIB Calabi-Yau compactifications, where the inflaton is a Kahler modulus parameterising the volume of an internal four-cycle. The inflaton potential is generated via poly-instanton corrections to the superpotential which give rise to a naturally flat direction due to their double exponential suppression. Given that the volume mode is kept stable during inflation, all the inflaton-dependent higher dimensional operators are suppressed. Moreover, string loop effects can be shown to be negligible throughout all the inflationary dynamics for natural values of the underlying parameters. The model is characterised by a reheating temperature of the order 10^6 GeV which requires about 54 e-foldings of inflation. All the inflationary observables are compatible with current observations since the spectral index is around 0.96, while the tensor-to-scalar ratio is of order 10^{−5}. The volume of the Calabi-Yau is of order 10^3 in string units, corresponding to an inflationary scale around 10^15 GeV.