Photon–axion mixing in an inhomogeneous universe

We consider the dimming of photons from high redshift type 1a supernovae through mixing with a pseudoscalar axion field in the intergalactic medium. We model the magnetic field and electron density using a log-normal probability distribution and frozen in magnetic fields. Assuming the magnetic fields are produced in the early universe we are unable to obtain sufficient dimming in order to explain the apparent acceleration without violating the bounds on the frequency dependence of the dimming. We also show that any axion mixing leading to a reduction in optical luminosities would also lead to a significant reduction in the polarisation of UV light from intermediate redshift objects which may be detected in the future.