Light spinless particle coupled to photons

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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 aγγ coupling. We examine the laboratory, as- trophysical 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) × U(1) gauge invariance, and analyze the phenomenological implications.