Thermal unparticles: a new form of energy density in the universe Shao-Long Chen, Xiao-Gang He, Xue-Peng Hu and Yi Liao Eur. Phys. J. C, 60 2 (2009) 317-321 Published online: 13 February 2009 DOI: 10.1140/epjc/s10052-009-0888-3