Axion Inflation in Type II String Theory

TL;DR

This paper explores axion-driven inflation within type IIB string theory, highlighting how multiple axions and string effects can produce viable inflation models with observable gravitational waves.

Contribution

It introduces a framework for axion inflation in type IIB compactifications, incorporating string corrections and instanton effects to generate suitable potentials and kinetic terms.

Findings

Large number of axions enable chaotic inflation over the entire field range.

String world-sheet corrections help achieve Planck-scale kinetic terms.

Potential for detectable gravitational waves with r<0.14.

Abstract

Inflationary models driven by a large number of axion fields are discussed in the context of type IIB compactifications with N=1 supersymmetry. The inflatons arise as the scalar modes of the R-R two-forms evaluated on vanishing two-cycles in the compact geometry. The vanishing cycles are resolved by small two-volumes or NS-NS B-fields which sit together with the inflatons in the same supermultiplets. String world-sheets wrapping the vanishing cycles correct the metric of the R-R inflatons. They can help to generate kinetic terms close to the Planck scale and a mass hierarchy between the axions and their non-axionic partners during inflation. At small string coupling, D-brane corrections are subleading in the metric of the R-R inflatons. However, an axion potential can be generated by D1 instantons or gaugino condensates on D5 branes. Models with sufficiently large number of axions admit regions of chaotic inflation which can stretch over the whole axion field range for potentials from gaugino condensates. These models could allow for a possibly detectable amount of gravitational waves with tensor to scalar ratio as high as r<0.14.