Universality Class of the Nishimori Point in the 2D ±J Random-Bond Ising Model

We study the universality class of the Nishimori point in the 2D ±J random-bond Ising model by means of the numerical transfer-matrix method. Using the domain-wall free energy, we locate the position of the fixed point along the Nishimori line at the critical concentration value p_c = 0.1094±0.0002 and estimate ν = 1.33±0.03. Then, we obtain the exponents for the moments of the spin-spin correlation functions as well as the value for the central charge c = 0.464±0.004. The main qualitative result is the fact that percolation is now excluded as a candidate for describing the universality class of this fixed point.