EQUIVALENCE AND COMPOSITENESS - BEYOND 1/NC IN 4-FERMION THEORIES

The equivalence between four-fermion and Yukawa models under the conditions Z3 = Z4 = 0 is rederived. These compositeness conditions are shown to be a simple self-consistent procedure for computing beyond the usual large-N(c) or fermion bubble approximation. In the case of the two-flavor Nambu-Jona-Lasinio model the 1/N(c) expansion is found to diverge for N(c) less-than-or-equal-to 24. The correct mass relationship and chiral-symmetry-restoration temperature T(c) are obtained as m(sigma)2 = 2m(q)2 + m(pi)2 and T(c) = f(pi).