Hagedorn singularity in exact $$ {\mathcal{U}}_{\textrm{q}}\left({\mathfrak{su}}_2\right) $$ S-matrix theories with arbitrary spins

Abstract

Abstract Generalizing the quantum sine-Gordon and sausage models, we construct exact S-matrices for higher spin representations with quantum $$ {\mathcal{U}}_{\textrm{q}}\left({\mathfrak{su}}_2\right) $$ U q su 2 symmetry, which satisfy unitarity, crossing-symmetry and the Yang-Baxter equations with minimality assumption, i.e. without any unnecessary CDD factor. The deformation parameter q is related to a coupling constant. Based on these S-matrices, we derive the thermodynamic Bethe ansatz equations for q a root of unity in terms of a universal kernel where the nodes are connected by graphs of non-Dynkin type. We solve these equations numerically to find out Hagedorn-like singularity in the free energies at some critical scales and find a universality in the critical exponents, all near 0.5 for different values of the spin and the coupling constant.