Dynamical symmetry breaking in four-fermion interaction models

Dynamical symmetry breaking in 4-fermion models in 2 + 1 dimensions is quantitatively studied. We use the 1/ N expansion and show that these models are renormalizable in this framework, in spite of their non-renormalizability in weak coupling expansion. The particular topics discussed include interactions of composite Goldstone bosons with other particles and among themselves, low-energy theorems, chiral lagrangians, the effects of explicit symmetry breaking, and the thermodynamics of the dynamical symmetry restoring phase transition.