A 331 WIMPy dark radiation model Chris Kelso, C. A. de S. Pires, Stefano Profumo, Farinaldo S. Queiroz and P. S. Rodrigues da Silva Eur. Phys. J. C, 74 3 (2014) 2797 Published online: 18 March 2014 DOI: 10.1140/epjc/s10052-014-2797-3