Backreaction Issues in Axion Monodromy and Minkowski 4-forms

TL;DR

This paper examines backreaction issues in axion monodromy models derived from string theory, highlighting differences from the Kaloper-Sorbo framework and exploring conditions under which the inflaton field range is limited.

Contribution

It clarifies the impact of field-dependent metrics on backreaction in axion monodromy and introduces open string fields as potential counter-examples to universal backreaction behavior.

Findings

Backreaction limits the inflaton field range to about the Planck scale in certain string compactifications.

Field dependence of the 3-form metric is crucial for understanding backreaction effects.

Open string fields can modify the backreaction behavior, providing potential ways to evade limitations.

Abstract

We clarify the differences between the usual Kaloper-Sorbo description of axion monodromy and the effective axionic potential in terms of Minkowski 4-forms derived in string compactifications. The fact that the metric of the 3-form fields coming from string theory is field dependent (unlike in Kaloper-Sorbo) leads to the backreaction issues recently studied in axion monodromy models within string theory. We reanalyse these problems in terms of the 4-forms focusing on the case in which the non-periodic scalars backreact on the Kahler metric of the inflaton reducing the physical field range. In the closed string sector of Type II Calabi-Yau compactifications with fluxes the metric becomes field dependent precisely when $\Delta\phi\sim M_p$, independently of the choice of fluxes. We propose, however, some counter-examples to this universal behaviour by including open string fields.