M. Dutsch et al., CAUSAL CONSTRUCTION OF YANG-MILLS THEORIES .1., Nuovo cimento della Società Italiana di Fisica. A. Nuclei, particles and fields, 106(8), 1993, pp. 1029-1041
Pure quantized Yang-Mills theories are constructed by causal-perturbat
ion theory. We study operator gauge transformations which lead in a na
tural way to the introduction of ghost fields. Considering fermionic a
s well as bosonic ghosts, we find that only the former save gauge inva
riance in second order. We work with free quantum fields throughout, s
o that all expressions are mathematically well defined.