Critical couplings for chiral symmetry breaking via instantons
  Using an instanton effective action formalism, we compute the critical coupling for the nonperturbative formation of a dynamical mass via instantons in non-Abelian gauge theories with N_f massless fermions. Only continuous phase transitions are considered. For large values of N_f the critical couplings are found to be much smaller than the equivalent critical couplings obtained from gauge exchange calculations in the ladder approximation. 
F. S. Roux