Ratio of Quark Masses in Duality Theories
  We consider N=2 SU(2) Seiberg-Witten duality theory for models with N_f=2 and N_f=3 quark flavors. We investigate arbitrary large bare mass ratios between the two or three quarks at the singular points. For N_f=2 we explore large bare mass ratios corresponding to a singularity in the strong coupling region. For N_f=3 we determine the location of both strong and weak coupling singularities that produce specific large bare mass ratios. 
G. Cleaver and K. Tanaka