Thermal form-factor approach to dynamical correlation functions of integrable lattice models

Abstract

We propose a method for calculating dynamical correlation functions at finite\ntemperature in integrable lattice models of Yang-Baxter type. The method is\nbased on an expansion of the correlation functions as a series over matrix\nelements of a time-dependent quantum transfer matrix rather than the\nHamiltonian. In the infinite Trotter-number limit the matrix elements become\ntime independent and turn into the thermal form factors studied previously in\nthe context of static correlation functions. We make this explicit with the\nexample of the XXZ model. We show how the form factors can be summed utilizing\ncertain auxiliary functions solving finite sets of nonlinear integral\nequations. The case of the XX model is worked out in more detail leading to a\nnovel form-factor series representation of the dynamical transverse two-point\nfunction.\n