The 1/N expansion method in quantum field theory

Abstract

The motivations of the 1/N expansion method in quantum field theory are explained. The method is first illustrated with the O(N) model of scalar fields. A second example is considered with the two-dimensional Gross-Neveu model of fermion fields with global U(N) and discrete chiral symmetries. The case of QCD is briefly sketched.

Comments: 26 pages, 13 figures. An introductory lecture given at the third International School "Symmetry in integrable systems and nuclear physics", 3-13 July 2013, Tsakhkadzor, Armenia