M and F-theory Instantons, N = 1 Supersymmetry and Fractional Topological Charge

We analize instanton generated superpotentials for three dimensional N=2 supersymmetric gauge theories obtained by compactifying on S1 N=1 four dimensinal theories. In the Nf = NC − 1 case, we find that the vacua in the decompactification limit is given by the singular points of the Coulomb branch of the N =2 four dimensional theory. The decompactification limit of the superpotential for pure gauge theories without chiral matter is interpreted in terms of ‘t Hooft’s fractional instanton amplitudes.