The Axion Helical Misalignment Mechanism

TL;DR

This paper introduces the axion helical misalignment mechanism, showing how primordial magnetic fields and chiral asymmetries can significantly alter axion relic abundance and contribute to baryogenesis.

Contribution

It provides a comprehensive analysis of how primordial magnetic fields and chiral effects modify axion evolution and relic abundance, a novel perspective in axion cosmology.

Findings

Primordial magnetic fields shift the onset of axion oscillations.

The axion helical misalignment mechanism alters relic abundance calculations.

Chiral magnetic effects can generate the Universe's baryon asymmetry.

Abstract

Understanding axion production in the early Universe remains a pivotal challenge, given the axion as a compelling cold dark matter candidate. Conventional misalignment scenarios often overlook the possibility that a large initial axion velocity can fundamentally reshape the subsequent evolution of the axion field. In this letter, we provide a comprehensive analysis of how primordial magnetic fields impact the axion relic abundance. By accounting for the axion coupling to the Chern-Simons term of the hypercharge gauge field, the equation of motion of the axion is recast as a driven oscillator equation. This modification effectively shifts the onset of axion oscillations, leading to a significant reevaluation of the final relic abundance, a novel effect we term the axion helical misalignment mechanism. Furthermore, in the presence of primordial chiral asymmetries, the chiral magnetic effect (CME) emerges as a critical driver of axion dynamics. The interplay between the axion field and the CME not only profoundly influences the evolution of Standard Model chiral fermions but also provides a viable pathway for generating the observed baryon asymmetry of the Universe.