  In this paper, we build on our previous work to further investigate the role
of evanescent operators in gauge theories, with a particular focus on their
contribution to violations of unitarity. We develop an efficient method for
calculating the norms of gauge-invariant operators in Yang-Mills (YM) theory by
employing on-shell form factors. Our analysis, applicable to general spacetime
dimensions, reveals the existence of negative norm states among evanescent
operators. We also explore the one-loop anomalous dimensions of these operators
and find complex anomalous dimensions. We broaden our analysis by considering
YM theory coupled with scalar fields and we observe similar patterns of
non-unitarity. The presence of negative norm states and complex anomalous
dimensions across these analyses provides compelling evidence that general
gauge theories are non-unitary in non-integer spacetime dimensions.
