Phenomenology of the companion-axion model: photon couplings
Zhe Chen (Sydney Consortium for Particle Physics and Cosmology, School of Physics, The University of Sydney, Sydney, NSW, 2006, Australia); Archil Kobakhidze (Sydney Consortium for Particle Physics and Cosmology, School of Physics, The University of Sydney, Sydney, NSW, 2006, Australia); Ciaran O’Hare (School of Physics, The University of Sydney and ARC Centre of Excellence for Dark Matter Particle Physics, Sydney, NSW, 2006, Australia); Zachary Picker (School of Physics, The University of Sydney and ARC Centre of Excellence for Dark Matter Particle Physics, Sydney, NSW, 2006, Australia); Giovanni Pierobon (School of Physics, The University of New South Wales, Sydney, NSW, 2052, Australia)
We study the phenomenology of the ‘companion-axion model’ consisting of two coupled QCD axions. The second axion is required to rescue the Peccei–Quinn solution to the strong-CP problem from the effects of colored gravitational instantons. We investigate here the combined phenomenology of axion–axion and axion–photon interactions, recasting present and future single-axion bounds onto the companion-axion parameter space. Most remarkably, we predict that future axion searches with haloscopes and helioscopes may well discover two QCD axions, perhaps even within the same experiment.
