Solution of the strong CP problem within QCD using the gradient flow

by Gerrit Schierholz (DESY)

Tuesday 25 Apr 2023, 16:00 → 18:00 Europe/Zurich

The strong CP problem is inseparably connected with the topology of gauge fields and the mechanism of color confinement, which requires nonperturbative tools to solve it. In this talk I present results of a recent lattice investigation of QCD with the $\theta$ term. The tool I am using to address the nonperturbative side of the problem is the gradient flow, which is a particular realization of momentum space RG transformations. The novel result is that within QCD the vacuum angle $\theta$ is renormalized in the IR, in combination with the strong coupling constant, and flows to $\theta = 0$ in the IR limit. This means that CP is conserved in the strong interactions. The Peccei-Quinn solution of the problem is commented.