Baryon Number Asymmetry Induced by Coherent Motions of a Cosmological Axion-Like Pseudoscalar

Abstract

A cosmological pseudoscalar field coupled to hypercharge topological number density can exponentially amplify hyperelectric and hypermagnetic fields in the symmetric phase of the electroweak plasma while coherently rolling or oscillating, leading to the formation of a condensate of topological number density. The topological number can be converted, under certain conditions, into baryon number in sufficient amount to explain the observed baryon asymmetry of the universe. We focus on a singlet elementary hypercharge axion (HCA) whose only coupling to standard model fields is to hypercharge topological number density. This model has two parameters: the mass $m$ and decay constant $M$ of the HCA. We describe this new mechanism for baryogenesis and outline the region of the parameter space in which the mechanism is efficient. We show that present colliders can already put interesting constraints on both parameters, and that future colliders will improve the detection capabilities very significatively.