  We consider decay of metastable topological configurations such as strings
and domain walls. The transition from a state with higher energy density to a
state with lower one proceeds through quantum tunneling or through thermally
catalyzed quantum tunneling (at sufficiently small temperatures). The
transition rate is calculated at zero temperature including the preexponential
factor and also at a finite low temperature. The thermal catalysis factor is
closely related to the probability (effective length) of destruction of the
string (the domain wall) in collisions of the Goldstone bosons, corresponding
to transverse waves on the string (wall). We derive a general formula which
allows to find the probability (effective length) of a string (wall) breakup by
a collision of arbitrary number of the bosons. We find that the destruction of
a string only takes place in collisions of even number of the bosons, while the
destruction of the wall can occur in a collision of any number of particles. We
explicitly calculate the energy dependence of such processes in two-particle
collisions for arbitrary relation between the energy and the largest infrared
scale (the size of a critical gap).
