Effects of initial axion production and photon--axion oscillation on   type Ia supernova dimming
  Recently, Csaki, Kaloper and Terning (CKT) suggested that axion-photon oscillation in the intergalactic medium can explain the observed dimming of distant type Ia supernovae. This mechanism works only if the initial axion flux is much smaller than the initial photon flux. We study several mechanisms for such initial axion production. The direct axion production in the supernovae, the photon-axion oscillation in the magnetic field of supernovae and in the magnetic field of their host galaxies are addressed. We find it likely that the initial axion flux is very small and therefore does not pose a problem to the CKT mechanism. 
Yuval Grossman, Sourov Roy, Jure Zupan