Domain walls of high-density QCD
  We show that in very dense quark matter there must exist metastable domain walls where the axial U(1) phase of the color-superconducting condensate changes by 2pi. The decay rate of the domain walls is exponentially suppressed and we compute it semiclassically. We give an estimate of the critical chemical potential above which our analysis is under theoretical control. 
D.T. Son, M.A. Stephanov, and A.R. Zhitnitsky