Runaway Relaxion Monodromy

TL;DR

This paper investigates the relaxion mechanism within string theory, revealing that monodromy charge backreaction disrupts the relaxion's ability to stabilize the Higgs vev, challenging its viability.

Contribution

It demonstrates that monodromy charge backreaction in string theory invalidates the relaxion mechanism by destroying the potential barriers needed for stopping the relaxion.

Findings

Backreaction of monodromy charge destroys relaxion barriers.

Relaxion cannot stop at the Higgs vev due to exponential suppression.

Technical naturalness arguments are limited in this context.

Abstract

We examine the relaxion mechanism in string theory. An essential feature is that an axion winds over $N \gg 1$ fundamental periods. In string theory realizations via axion monodromy, this winding number corresponds to a physical charge carried by branes or fluxes. We show that this monodromy charge backreacts on the compact space, ruining the structure of the relaxion action. In particular, the barriers generated by strong gauge dynamics have height $\propto e^{-N}$, so the relaxion does not stop when the Higgs acquires a vev. Backreaction of monodromy charge can therefore spoil the relaxion mechanism. We comment on the limitations of technical naturalness arguments in this context.