GUT-scale inflation with sizeable tensor modes

TL;DR

This paper explores how F-term hybrid inflation models can be embedded in supergravity to produce a sizeable tensor-to-scalar ratio, aligning with recent BICEP2 claims, while maintaining a sub-Planckian field excursion.

Contribution

It demonstrates a UV embedding of F-term hybrid inflation in supergravity that allows for large tensor modes with sub-Planckian field excursions through tuning higher-order operators.

Findings

Potential for sizeable tensor fluctuations in F-term hybrid inflation

Sub-Planckian field excursions compatible with large tensor modes

Alignment with BICEP2's claimed tensor-to-scalar ratio

Abstract

A sizeable tensor-to-scalar ratio, such as recently claimed by BICEP2, would imply a scale of inflation at the typical scale of supersymmetric grand unification. This could be an accident, or strong support for supersymmetric theories. Models of F-term hybrid inflation naturally connect the GUT scale with the inflationary scale, but they also predict the tensor-to-scalar ratio to be unmeasurably small. In this work we analyze a general UV embedding of F-term hybrid inflation into a supergravity theory with a general Kahler potential. The CMB observables are generated during the early phase of inflation, at large inflaton values, where the potential is dominated by Planck-suppressed operators. Tuning the leading higher-order terms can give an inflaton potential with sizeable tensor fluctuations and a field excursion which is still sub-Planckian but close to the Planck scale, as expected from the Lyth bound.