Using the Bethe-ansatz method we analyze the thermodynamic properties of the massive Thirring model in the zero-charge-sector attractive case, including the "charged vacuum" excitations introduced by Korepin. The energy of these excitations is calculated as a function of momentum and temperature and agrees with Korepin's results at
T=0. The specific heat is presented and shown to vary smoothly for the whole range of coupling in the attractive regime.
We propose a model that describes approximately the strong-coupling limit of interacting electrons and holes in a one-dimensional quantum wire. An exact solution for this model at the SU ( n ) symmetric point of equal electron and hole masses and for a particular ratio of the forward- ( f ) to backward-scattering ( g ) is obtained by means of the Bethe ansatz. The model discussed is a hybrid between the chiral invariant Gross-Neveu model of quantum chromodynamics and the massive Thirring model. While the eigenstates exhibit a huge degeneracy in colour (spin) space as in the U → ∞ Hubbard model, the charge excitation spectrum comprizes excitons, bi-excitons and other electron-hole complexes (droplets) for not too repulsive interactions ( − 2/√3 ⩽ g ⩽ − 1). In the regime of strong repulsion ( g < − 2/√3), the bi-excitons and large droplets disappear from the spectrum.