Cosmic Acceleration Vs Axion-photon Mixing

Axion-photon mixing has been proposed as an alternative to acceleration as the explanation for supernovae dimming. We point out that the loss of photons due to this mixing will induce a strong asymmetry between the luminosity, dL(z), and angular-diameter distance, dA(z), since the latter is unaffected by mixing. In a first search for such asymmetry we introduce an amplitude A, such that A = 1 if no photons are lost and A = 0.81 if axion-photon mixing occurs. The best-fit to a subset of SNIa and radio galaxy data at z > 0.5 is A = 0.97 ± 0.17 (1σ). This same argument limits the attenuation of light from supernovae due to dust. We show that future dL and dA data from SNAP and galaxy surveys such as DEEP2 and KAOS will detect or rule out mixing at more than 4σ, almost independently of the dark energy dynamics. Finally we discuss the constraints from the near maximal polarisation of the gamma-ray burst (GRB) GRB021206. Since mixing reduces the polarisation of distant sources, future observations of high redshift GRBs will provide orthogonal constraints on axion-photon mixing and related scenarios. Subject headings: Cosmology: cosmological parameters