Abstract:
The standard lore posits that pure QCD dynamics generates a confining potential with a branched structure as a function of the θ angle. This same potential also largely determines the properties of the η′, the (would-be) Goldstone boson associated with the anomalous axial U(1) symmetry of QCD, once fermions are included. In this talk I will describe how this picture can be tested by examining a supersymmetric extension of QCD with a small amount of supersymmetry breaking generated via anomaly mediation. I will demonstrate that for pure SU(N) QCD without flavors there are N branches generated by gaugino condensation. However, once quarks are introduced, flavor effects qualitatively change the strong dynamics, leading to |N-F| branches for F flavors. I will also show that for F=N-1,N,N+1 there are no branches and the entire potential is consistent with being a one-instanton effect. Finally I will comment on spontaneous CP breaking in the theory with one flavor. This talk will be based on arXiv:2307.04809.