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, Lambda similar to 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 ultralight (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 for Delta t(m gamma=0), the duration of the epoch stretching from the present to the point where the photon starts to be Meissner massive, is obtained: Delta t(m gamma=0) similar to 2.2 billion years.