Poly-instanton inflation

Abstract

We propose a new inflationary scenarioin type IIB Calabi-Yau compactifications,where the inflaton is a Kähler modulus parameterising the volume of an internal four-cycle.The inflaton potential is generated via poly-instanton corrections to the superpotential whichgive 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 shownto be negligible throughout all the inflationarydynamics for natural values of the underlying parameters.The model is characterised by a reheating temperatureof the order Trh ≃ 106 GeV which requires Ne ≃ 54 e-foldings of inflation.All the inflationary observables are compatible with current observationssince the spectral index is ns ≃ 0.96,while the tensor-to-scalar ratio is r ≃ 10−5.The volume of the Calabi-Yau is of order 103 in string units,corresponding to an inflationary scale around 1015 GeV.