QUANTUM-FIELD THEORIES IN FINITE-VOLUME - EXCITED-STATE ENERGIES

We develop a method of computing the excited state energies in Integra ble Quantum Field Theories (IQFT) in finite geometry, with the spatial coordinate compactified on a circle of circumference R. The IQFT ''co mmuting transfer matrices'' introduced earlier [Commun. Math. Phys. 17 7 (1996) 381] for Conformal Field Theories (CFT) are generalized to no n-conformal IQFT obtained by perturbing CFT with the operator Phi(1,3) . We study the models in which the fusion relations for these ''transf er matrices'' truncate and provide closed integral equations which gen eralize the equations of the thermodynamic Bethe ansatz to excited sta tes. The explicit calculations are done for the first excited state in the ''scaling Lee-Yang model''. (C) 1997 Elsevier Science B.V.