Challenges for D-brane large-field inflation with stabilizer fields

TL;DR

This paper investigates string theory models for large-field inflation with stabilizer fields, finding tachyonic instabilities in type IIA setups and challenges in hierarchy in type IIB models, highlighting key obstacles in realizing consistent inflation.

Contribution

It identifies fundamental issues in string compactifications for large-field inflation, especially the emergence of tachyonic directions and hierarchy challenges, guiding future model building.

Findings

Tachyonic directions arise in type IIA models after moduli integration.

Shift symmetries in type IIA Kähler potential hinder stabilization.

Hierarchy problems prevent successful inflation in type IIB setups.

Abstract

We study possible string theory compactifications which, in the low-energy limit, describe chaotic inflation with a stabilizer field. We first analyze type IIA setups where the inflationary potential arises from a D6-brane wrapping an internal three-cycle, and where the stabilizer field is either an open-string or bulk K\"ahler modulus. We find that after integrating out the relevant closed-string moduli consistently, tachyonic directions arise during inflation which cannot be lifted. This is ultimately due to the shift symmetries of the type IIA K\"ahler potential at large compactification volume. This motivates us to search for stabilizer candidates in the complex structure sector of type IIB orientifolds, since these fields couple to D7-brane Wilson lines and their shift symmetries are generically broken away from the large complex structure limit. However, we find that in these setups the challenge is to obtain the necessary hierarchy between the inflationary and Kaluza-Klein scales.