Abstract:
The strong CP problem, i.e., the question why the CP violation by the strong interaction is smaller than 10^-10, is one of the most important problems in the Standard Model. There are two potential sources of CP violation in QCD, namely complex chiral phases in the quark mass matrix and the so-called 't Hooft vertex, which arises from instanton effects. Only one of them can be removed by field redefinitions, meaning that QCD should violate CP unless the chiral phases in these two terms happen to be aligned. In this talk, I will discuss a recent computation of the fermionic correlation functions in the θ vacuum in which we find such an alignment. If our approach is correct the phases can be removed by chiral rotations of quarks, and thus there is no physical CP violation in QCD.