Dyon dynamics near marginal stability and non-BPS states

We derive the general form of the moduli-space effective action for the long-range interaction of two BPS dyons in N=2N=2 gauge theories. This action determines the bound state structure of various BPS and non-BPS states near marginal stability curves, and we utilise it to compute the leading correction to the BPS-mass of zero-torsion non-BPS bound states close to marginal stability.