Circumventing the eta problem in building an inflationary model in string theory

TL;DR

This paper addresses the eta problem in string theory inflation models, demonstrating that non-minimal coupling and DBI kinetic terms can avoid it, with potential observational signatures in CMB non-gaussianities.

Contribution

It shows that the eta problem can be circumvented in string inflation models through non-minimal coupling and DBI kinetic terms, supported by exact numerical solutions.

Findings

The eta problem can be avoided with non-minimal coupling and DBI kinetic terms.

CMB non-gaussianities can probe scalar-gravity couplings.

Numerical solutions demonstrate the viability of these scenarios.

Abstract

The eta problem is one of the most significant obstacles to building a successful inflationary model in string theory. Planck mass suppressed corrections to the inflaton potential generally lead to inflaton masses of order the Hubble scale and generate contributions of order unity to the eta slow roll parameter rendering prolonged slow roll inflation impossible. We demonstrate the severity of this problem in the context of brane anti-brane inflation in a warped throat of a Calabi-Yau flux compactification with all phenomenologically dangerous moduli stabilized. Using exact numerical solutions we show that the eta problem can be avoided in scenarios where the inflaton is non-minimally coupled to gravity and has Dirac-Born-Infeld (DBI) kinetic term. We show that the resulting cosmic microwave background (CMB) observables such as measures of non-gaussianites can, in principle, serve as a probe of scalar-gravity couplings.