On Mass-Deformed N=4 Supersymmetric Yang-Mills Theory

We construct the n-instanton action for the above model with gauge group SU(2), as a function of the collective coordinates of the general self-dual configurations of Atiyah, Drinfeld, Hitchin and Manin (ADHM). We calculate the quantum modulus u = at the 1-instanton level, and find a discrepancy with Seiberg and Witten's proposed exact solution. As in related models (N=2, N_F=3 or 4), this discrepancy may be resolved by modifying their proposed relation between $\tilde u$ (the parameter in the elliptic curve) and u.