Low-Temperature Nucleation in a Kinetic Ising Model with Soft Stochastic Dynamics

We study low-temperature nucleation in kinetic Ising models by analytical and simulational methods, confirming the general result for the average metastable lifetime, ⟨τ⟩=Aexp(βΓ) (β=1/kBT) [E. Jord\~ao Neves and R. H. Schonmann, Commun. Math. Phys. 137, 209 (1991)]. Contrary to common belief, we find that both A and Γ depend significantly on the stochastic dynamic. In particular, for a ``soft'' dynamic, in which the effects of the interactions and the applied field factorize in the transition rates, Γ does not simply equal the energy barrier against nucleation, as it does for the standard Glauber dynamic, which does not have this factorization property.