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.Comment: 4 pages, 4 figures. To appear in the proceedings of 7th Patras
Workshop on Axions, WIMPs and WISPs, Mykonos, Greece, 26 June - 1 July 2011
and of TAUP 2011, Munich, Germany, 5 - 9 September 201
