EXACT RESULTS FOR THE CRITICAL-BEHAVIOR OF A NIENHUIS O(N) MODEL ON THE SQUARE LATTICE

Exact results are obtained for a square lattice fifteen-vertex model and related O(n) model recently proposed by Nienhuis. The partition function per site and finite-size corrections are obtained, along with the critical exponents via the Temperley-Lieb equivalent six-vertex model. The exact exponents nu = 4/7 and gamma = 6/7 follow in the limit n = 0 for even system sizes. Odd system sizes are also discussed. The fifteen-vertex model is also the vertex formulation of the anisotropic, or q-deformed, spin-1 biquadratic model.