On N=2 Supersymmetric QCD with 4 Flavors

Seiberg and Witten's proposed solution of N=2 SQCD with N_c=2 and N_F=4 is known to conflict with instanton calculations in three distinct ways. Here we show how to resolve all three discrepancies, simply by reparametrizing the elliptic curve in terms of quantities $\tau^0_{eff}$ and $\tilde{u}$ rather than $\tau$ and $u = < Tr A^2 >$. SL(2,Z) invariance of the curve is preserved. However, there is now an infinite ambiguity in the relation between $\tau^0_{eff}$ and $\tau$ and between $\tilde{u}$ and $u$, corresponding to an infinite number of unknown coefficients in the instanton expansion. Thus the reinterpreted curve (unlike the cases N_F<4) no longer determines the quantum modulus u as a function of the classical VEV a.