Quantum-invariant theory and the evolution of a Dirac field in Friedmann–Robertson–Walker flat space-times Xiao-Chun Gao, Jian Fu and Jian-Qi Shen Eur. Phys. J. C, 13 3 (2000) 527-541 Published online: 06 March 2000 DOI: 10.1007/s100520000257