Cosmic axion background

Abstract

Axions, hypothetical particles ubiquitous in theories of particle physics, can be produced in great profusion in the early Universe and remain relativistic to the present day, forming a relic background - a cosmic axion background (CaB). In the present paper, Jeff A. Dror, Hitoshi Murayama, and Nicolas L. Rodd explore different production mechanisms of relativistic relic axions and the potential of their discovery with extant and future experiments. They show that experiments can have sensitivities relevant to the CaB and, therefore, serve as probes of the history of the Universe.