Problems with duality in N=2 super-Yang-Mills theory

Paper in proceeding, 1996

Actual calculations of monopole and dyon spectra have previously been performed in N=4 SYM and in N=2 SYM with gauge group SU(2), and are in total agreement with duality conjectures for the finite theories. These calculations are extended to N=2 SYM with higher rank gauge groups, and it turns out that the SU(2) model with four fundamental hypermultiplet is an exception in that its soliton spectrum supports duality. This may be an indication that the other perturbatively finite N=2 theories have non-perturbative contributions to the beta-function. This talk contains a short summary of recent results.