Abstract
The longstanding problem of thermal pair nucleation in the presence of global reflection symmetry (viz. no external biases) is investigated numerically for a ϕ4 classical string coupled to a viscous heat bath. Our numerics agree within a few percent with the theoretical estimates for the low-temperature kink (antikink) density; as a result, finite-temperature corrections could be assessed quantitatively. More importantly, the relevant pair nucleation rates, too, have been computed numerically, thus confirming the predictions of the kinetic model: Local symmetry breaking by pre-existing kinks (antikinks) assists the nucleation of new kink-antikink pairs in the stationary regime and determines their lifetime.