Cosmological constraints on thermal relic axions and axion-like   particles
  Cosmological precision data can be used to set very strict constraints on Axions and Axion-like particles (ALPs) produced thermally in the big bang. We briefly review the known bounds and propose two new constraints for Axions and ALPs decaying in the early universe, based upon the concomitant dilution of baryon and neutrino densities, using WMAP7 and other cosmological data. 
Davide Cadamuro, Javier Redondo
hep-ph