From S-matrices to the Thermodynamic Bethe Ansatz

Abstract

We derive the TBA system of equations from the S-matrix describing integrable massive perturbation of the coset $G_l \times G_m / G_{l+m}$ by the field $(1,1,adj)$ for all the infinite series of the simple Lie algebras $G=A,B,C,D$. In the cases A,C, where the full S-matrices are known, the derivation is exact, while B,D cases dictate some natural assumption about the form of the crossing- -unitarizing prefactor for any two fundam. reps of the algebras. In all the cases the derived systems are transformed to the corresponding functional Y-system and shown to have the correct high temperature (UV) asymptotic in the ground state, reproducing the correct central charge of the coset. Some specific particular cases of the considered S-matrices are discussed.