FINITE-TEMPERATURE SCHWINGER MODEL WITH CHIRALITY BREAKING BOUNDARY-CONDITIONS

The N-t-Flavour Schwinger Model on a finite space 0 less than or equal to x(1) less than or equal to L and subject to bag-type boundary-cond itions at x(1) = 0 and x(1) = L is solved at finite temperature T = 1/ beta. The boundary conditions depend on a real parameter (I and break the axial flavour symmetry. We argue that this approach is more approp riate to study the broken phases than introducing small quark masses, since all calculations can be performed analytically. In the imaginary time formalism we determine the thermal correlators for the fermion-f ields and the determinant of the Diracoperator in arbitrary background gauge-fields. We show that the boundary conditions induce a CP-odd th eta-term in the effective action. The chiral condensate, and in partic ular its T- and L-dependence, is calculated for N-f fermions. It is se en to depend on the order in which the two lengths beta = 1/T and L ar e sent to infinity. (C) 1997 Academic Press.