New Instanton Effects in Supersymmetric QCD

In supersymmetric QCD with SU(Nc) gauge group and Nf flavors, it is known that instantons generate a superpotential if Nf = Nc−1 and deform the moduli space of vacua if Nf = Nc. But the role of instantons has been unclear for Nf > Nc. In this paper, we demonstrate that for Nf > Nc, on the moduli space of vacua, instantons generate a more subtle chiral operator containing (for example) non-derivative interactions of 2(Nf−Nc)+4 fermions. Upon giving masses to some flavors, one can integrate out some fermions and recover the standard results for Nf = Nc and Nf = Nc − 1. For Nf = Nc, our analysis gives, in a sense, a more systematic way to demonstrate that instantons deform the complex structure of the moduli space of vacua.