A Planck-scale axion and SU(2) Yang-Mills dynamics: Present acceleration and the fate of the photon

From the time of CMB decoupling onwards we investigate cosmological evolution subject to a strongly interacting SU(2) gauge theory of Yang-Mills scale Λ ∼ 10−4 eV (masquerading as the U(1)Y factor of the SM at present). The viability of this postulate is discussed in view of cosmological and (astro)particle physics bounds. The gauge theory is coupled to a spatially homogeneous and ultra-light (Planck-scale) axion field. As first pointed out by Frieman et al., such an axion is a viable candidate for quintessence, i.e. dynamical dark energy, being associated with today’s cosmological acceleration. A prediction of an upper limit ∆tmγ=0 for the duration of the epoch stretching from the present to the point where the photon starts to be Meissner massive is obtained: ∆tmγ=0 ∼ 2.2 billion years.