String Junctions and BPS States in Seiberg-Witten Theory
  We argue that certain BPS states in the D3-brane probe realization of N=2 SU(2) Super-Yang-Mills theory correspond to multi-pronged strings connecting the D3-brane to the background 7-branes. This provides a physical realization of the decay of these states on the curve of marginal stability, and explains their absence in the strong coupling regime. 
O. Bergman (Harvard), A. Fayyazuddin (Harvard)