The Nonperturbative Gauge Coupling of N=2 Supersymmetric Theories
  We argue that the topology of the quantum coupling space and the low energy effective action on the Coulomb branch of scale invariant N=2 SU(n) gauge theories pick out a preferred nonperturbative definition of the gauge coupling up to non-singular holomorphic reparametrizations. 
Philip C. Argyres and Alex Buchel