In the Euclidean QFT obtained by "Wick-rotating" a unitary QFT, the correlation functions satisfy a property called reflection positivity, see e.g. this Wikipedia article for the case of a scalar field.
What's the correct formulation if you have chiral fermions and/or terms like the QCD theta angle? Could someone give the references?
This post imported from StackExchange Physics at 2014-04-05 04:30 (UCT), posted by SE-user Yuji