# Axion Misalignment Driven to the Bottom

## TL;DR

This paper proposes a dynamical mechanism within supersymmetric theories that naturally drives the axion misalignment angle to small values, addressing overproduction issues and damping isocurvature perturbations in high decay constant axion models.

## Contribution

It introduces a new dynamical process involving early strong dynamics and Higgs-inflaton coupling that reduces the axion misalignment angle without fine-tuning.

## Key findings

- Axion field is driven to the potential minimum before QCD transition.
- Isocurvature perturbations are effectively damped by the relaxation mechanism.
- Supersymmetric models can realize this damping within inflationary cosmology.

## Abstract

Several theoretical motivations point to ultralight QCD axions with large decay constants $f_a \simeq \mathcal{O}(10^{16}-10^{17})$ GeV, to which experimental proposals are dedicated. This regime is known to face the problem of overproduction of axion dark matter from the misalignment mechanism unless the misalignment angle $\theta_{\rm mis}$ is as small as $\mathcal{O}(10^{-3}-10^{-4})$, which is generally considered a fine-tuning problem. We investigate a dynamical explanation for a small $\theta_{\rm mis}$. The axion mass arises from strong dynamics and may be sufficiently enhanced by early dynamics so as to overcome Hubble friction and drive the field value to the bottom of the potential long before the QCD phase transition. Together with an approximate CP symmetry in the theory, this minimum is very closely related to today's value and thus $\theta_{\rm mis}$ can automatically be well under unity. Owing to such efficient relaxation, the isocurvature perturbations are essentially damped. As an existence proof, using supersymmetric theories we illustrate that the Higgs coupling with the inflaton energy can successfully achieve this axion damping in a consistent inflationary cosmology.