Singular SQCD Vacua and Confinement

Abstract: We revisit the study of confining vacua in the softly broken N=2 supersymmetric QCD, in the light of some recent developments in our understanding of the dynamics of N=2 gauge theories. These vacua are characterized by an effective magnetic $SU(r)$ gauge group ($0\leq r\leq N_f/2$) and are referred to sometimes as the $r$ vacua. We further clarify the meaning of $r \leftrightarrow N_{f}-r$ duality arising from the matching of semi-classical and quantum vacua. A particular attention is paid to certain singular SCFT's of N=2 SQCD, driven into confinement phase by the adjoint mass deformation $\mu\, \Phi^{2}$. In some cases they occur as a result of coalescence of different $r$ vacua as the bare mass is tuned to a critical value.