Dynamic critical exponents of the Ising model with multispin interactions

We revisit the short-time dynamics of 2D Ising model with three spin interactions in one direction and estimate the critical exponents z, theta, beta and nu. Taking properly into account the symmetry of the Hamiltonian, we obtain results completely different from those obtained by Wang et al.(10) For the dynamic exponent z our result coincides with that of the 4-state Potts model in two dimensions. In addition, results for the static exponents nu and beta agree with previous estimates obtained from finite size scaling combined with conformal invariance. Finally, for the new dynamic exponent theta we find a negative and close to zero value, a result also expected for the 4-state Potts model according to Okano et al.