On a Light Spinless Particle Coupled to Photons

Abstract

A pseudoscalar or scalar particle $ϕ$ that couples to two photons but not to leptons, quarks and nucleons would have effects in most of the experiments searching for axions, since these are based on the $a γγ$ coupling. We examine the laboratory, astrophysical and cosmological constraints on $ϕ$ and study whether it may constitute a substantial part of the dark matter. We also generalize the $ϕ$ interactions to possess $SU(2) \times U(1)$ gauge invariance, and analyze the phenomenological implications.