Professor Joseph Conlon introduces the general idea of axions: particles associated to fields which are valued on a circle rather than a real line. He describes the still unresolved strong CP problem of the Standard Model, for which the so-called QCD axion provides the most plausible solution. He explains the typical coupling of particle physics axions to electromagnetism and how this leads to axion-photon conversion in magnetic fields and potential search strategies for axions.
