Non-Perturbative Decay of a Monopole: the Semiclassical Pre-Exponential Factor

The rate of the non-perturbative decay of a 't Hooft - Polyakov monopole in an external electric field into a dyon and a charged fermion is calculated. The subleading semiclassical prefactor is presented for the first time for this process. The leading exponential factor is shown to be in full agreement with the previous results derived in a different technique. Analogous treatment is shown to hold for the two-fermionic decay of the lightest bound state in Thirring model, allowing one to restore the "effective meson - fermion vertex".