arXiv:math-ph/9912014 · International Journal of Modern Physics A
THERMODYNAMIC BETHE ANSATZ EQUATION FROM FUSION HIERARCHY OF osp (1|2) INTEGRABLE SPIN CHAIN
KAZUMITSU SAKAI, ZENGO TSUBOI
Abstract
The thermodynamic Bethe ansatz (TBA) and the excited state TBA equations for an integrable spin chain related to the Lie superalgebra osp (1|2) are proposed by the quantum transfer matrix (QTM) method. We introduce the fusion hierarchy of the QTM and derive the functional relations among them (T-system) and their certain combinations (Y-system). Their analytical property leads to the nonlinear integral equations which describe the free energy and the correlation length at any finite temperatures. With regard to the free energy, they coincide with the TBA equation based on the string hypothesis.