Branes and supersymmetry breaking in 3D gauge theories

It is shown that supersymmetry is spontaneously broken in certain three-dim ensional supersymmetric gauge theories, by using the s-rule in their string theory realization as brane configurations. In particular, supersymmetry i s broken in N = 3 supersymmetric Yang-Mills-Chern-Simons theory with gauge group SU(n) and CS coefficient k, as well as in its N = 2 and N = 1 deforma tions, when n > \k\. In addition, supersymmetry is broken in the N = 1 mass deformation of N = 2 supersymmetric Yang-Mills theory with gauge group SU( n) and one matter multiplet when n >1. In the latter case the breaking is i nduced by an instanton-generated repulsive potential.