Chiral symmetry at finite temperature: Linear versus nonlinear [Formula presented] models

The linear [Formula presented] [Formula presented] model undergoes a symmetry-restoring phase transition at finite temperature. We show that the nonlinear [Formula presented] [Formula presented] model also undergoes a symmetry-restoring phase transition; the critical temperatures are the same when the linear model is treated in the mean field approximation and the nonlinear model is treated to leading plus subleading order in the [Formula presented] expansion. We also carefully define and study the behavior of [Formula presented] and the scalar condensate at low temperatures in both models, showing that they are independent of field redefinition.