Constraints on supernovae dimming from photon-pseudo scalar coupling
  An alternative mechanism that dims high redshift supernovae without cosmic acceleration utilizes an oscillation of photons into a pseudo-scalar particle during transit. Since angular diameter distance measures are immune to the loss of photons, this ambiguity in interpretation can be resolved by combining CMB acoustic peak measurements with the recent baryon oscillation detection in galaxy power spectra. This combination excludes a non-accelerating dark energy species at the 4sigma level regardless of the level of the pseudo-scalar coupling. While solutions still exist with substantial non-cosmological dimming of supernovae, they may be tested with future improvement in baryon oscillation experiments. 
Yong-Seon Song, Wayne Hu (KICP, U. Chicago)