Metastable lifetimes in a kinetic Ising model: Dependence on field and system size

The lifetimes of metastable states in kinetic Ising ferromagnets are studied\nby droplet theory and Monte Carlo simulation, in order to determine their\ndependences on applied field and system size. For a wide range of fields, the\ndominant field dependence is universal for local dynamics and has the form of\nan exponential in the inverse field, modified by universal and nonuniversal\npower-law prefactors. Quantitative droplet-theory predictions are numerically\nverified, and small deviations are shown to depend nonuniversally on the\ndetails of the dynamics. We identify four distinct field intervals in which the\nfield dependence and statistical properties of the lifetimes are different. The\nfield marking the crossover between the weak-field regime, in which the decay\nis dominated by a single droplet, and the intermediate-field regime, in which\nit is dominated by a finite droplet density, vanishes logarithmically with\nsystem size. As a consequence the slow decay characteristic of the former\nregime may be observable in systems that are macroscopic as far as their\nequilibrium properties are concerned.\n