Using a Hamiltonian formulation of the master equation, we carry out finite-size calculations for the dynamical critical exponent
z of the kinetic Ising model in one and two dimensions. In one dimension, different appropriately normalized transition probabilities give different values for
z; this result is based on both exact and finite-size calculations. We show that this "nonuniversal" behavior is due to the fact that the critical temperature for the one-dimensional Ising model is zero. In two dimensions we combine our finite-size calculations with finite-size scaling theory to calculate
z. Even in this case we find that
z depends on the form of the transition probability---a result that contradicts the universality hypothesis for dynamical critical behavior. We discuss the possible reasons for this contradiction.
We investigate the static and dynamic critical behaviour of a uniformly driven bilayer Ising lattice gas at half-filling. Depending on the strength of the inter-layer coupling J , phase separation occurs across or within the two layers. The former transitions are controlled by the universality class of model A (corresponding to an Ising model with Glauber dynamics), with upper critical dimension d c = 4. The latter transitions are dominated by the universality class of the standard (single-layer) driven Ising lattice gas, with d c = 5 and a nonclassical anisotropy exponent. These two distinct critical lines meet at a nonequilibrium bicritical point which also falls into the driven Ising class. At all transitions, novel couplings and dangerous irrelevant operators determine corrections to scaling.
A new Monte Carlo dynamics is proposed for ${\mathrm{\ensuremath{\varphi}}}^{4}$ field theory that reduces critical slowing down. Discrete Ising variables are embedded into the field theory, so that large-scale tunneling events can be induced via a modified Swendsen-Wang algorithm with fluctuating site-bond percolation probabilities. The measured dynamical critical exponents ${\mathrm{z}}_{\mathrm{EL}=0.07\ifmmode\pm\else\textpm\fi{}}$0.07, 0.29\ifmmode\pm\else\textpm\fi{}0.09, and 0.87\ifmmode\pm\else\textpm\fi{}0.20 in one, two, and three dimensions, respectively, are consistent with our conjecture that this embedded dynamics lies in the same universality class as the Swendsen-Wang Ising dynamics.