The Dynamical Mixing of Light and Pseudoscalar Fields

We solve the general problem of mixing of electromagnetic and scalar or pseudoscalar fields coupled by axion-type interactions Lint = gφφ ǫμναβF μνFαβ . The problem depends on several dimensionful scales, including the magnitude and direction of background magnetic field, the pseudoscalar mass, plasma frequency, propagation frequency, wave number, and finally the pseudoscalar coupling. We apply the results to the first consistent calculations of the mixing of light propagating in a background magnetic field of varying direction, which shows a great variety of fascinating resonant and polarization effects. For about 20 years the mixing of light and pseudoscalar fields in propagation has been studied with fascination [1]-[7]. The subject generated renewed attention in the context of cosmological observables that can probe exceedingly small couplings [8, 9, 10, 11]. One recent approach proposes that the dimming of supernova light might be explained by transition of light into unobserved pseudoscalar, or