The decorated star-triangle relation (DSTR) discussed by Shastry is extended into the general free-fermion model. Using the trigonometric limit of the DSTR, we construct a new solvable bilayer vertex model. The relation between the DSTR and the tetrahedral Zamolodchikov algebra is discussed.
In this paper we present a new solution of the star-triangle relation having positive Boltzmann weights. The solution defines an exactly solvable two-dimensional Ising-type (edge interaction) model of statistical mechanics where the local “spin variables” can take arbitrary integer values, i.e., the number of possible spin states at each site of the lattice is infinite. There is also an equivalent “dual” formulation of the model, where the spins take continuous real values on the circle. From algebraic point of view this model is closely related to the to the 6-vertex model. It is connected with the construction of an intertwiner for two infinite-dimensional representations of the quantum affine algebra Uq(slˆ(2)) without the highest and lowest weights. The partition function of the model in the large lattice limit is calculated by the inversion relation method. Amazingly, it coincides with the partition function of the off-critical 8-vertex free-fermion model.
A new type of Yang-Baxter equation (YBE) for R-operators depending on three spectral parameters is constructed from the star-triangle relation for the chiral Potts model. As the ZN symmetric generalization to the Ising model, its Boltzmann weights are known to depend on two variables describing a curve with genus larger than one for N>2, except for the self-dual point corresponding to the Fateev-Zamolodchikov chain. Combined with the fact that quantum Hamiltonians of edge-type models such as the Ising model contain both nearest-neighbor interaction and onsite potential terms, this leads naturally to an additional spectral parameter in the associated R-operator. The construction extends the edge-vertex correspondence of solvable lattice models, and provides a bridge between the Bazhanov-Stroganov four-parameter R-matrix---realized as an intertwiner of cyclic representations of Uq(sl2) at a root of unity---and Shastry's two-parameter R-operator obtained from the decorated YBE.