The (2+1)-dimensional NJL model at finite temperature

We decribe properties of (2 + 1)-dimensional Nambu-Jona-Lasinio (NJL) model s at finite temperature, beginning with the model with a discrete chiral sy mmetry. We then consider the model with a continuous U(1) x U(1) chiral sym metry, describing the restoration of the symmetry at finite temperature. In each case, we compute the free energy and comment on a recently proposed c onstraint based upon it. We conclude with a brief discussion of NJL models with larger chiral symmetries. (C) 2000 Published by Elsevier Science B.V.