Hello Community! I can't find a good answer(if there is) to my question. When in statistical mechanics we can define the order parameter for to study some phase transition. we need to define a order parameter. Now, I want to know if we can to define/find some "order parameter" for to study the phase transition in a Gauge Theory, for example, in QCD, which is a Gauge Theory and there we have different phase transition. Then, a Order Parameter in a Gauge Theory: Can we find/define one in a Gauge Theory(like QCD)??? I hope some comment. Thank you!