Chiral symmetry, 1/N expansion and low energy quantum chromodynamics

In these notes the authors explore the long distance effective Lagrangian for QCD. The general scenario is to look for the lagrangian that describes weakly coupled degrees of freedom. The non-linear sigma model has been widely discussed in the literature as a viable candidate. The authors discuss this but eventually argue that the linear sigma model can provide a better alternative. They discuss the following topics: (i) QCD chiral symmetries and Landau-Ginzburg type effective Lagrangian; (ii) Baryons as solitons and the Skyrme model; (iii) Wess-Zumino term; (iv) Consequences of the Wess-Zumino term; (v) Quantization of the Skyrme soliton; (vi) Nambu-Jona-Lasinio Model