Prepotentials in N = 2 SU(2) supersymmetric Yang-Mills theory with massless hypermultiplets

We calculate the prepotential of the low-energy effective action for N = 2 SU(2) supersymmetric Yang-Mills theory with Nf massless hypermultiplets (Nf = 1, 2, 3). The precise evaluation of the instanton corrections is performed by making use of the Picard-Fuchs equations associated with elliptic curves. The flavor dependence of the instanton effect is determined explicitly both in the weak- and strong-coupling regimes.