  We demonstrate numerically that an oscillation mode in 1+1 dimensions (eg a
breather or an oscillon) can decay into a kink-antikink pair by a sudden
distortion of the evolution potential which occurs within a certain time or
space domain. In particular, we consider the transition of a sine-Gordon
potential into a \Phi^4 potential. The breather field configuration is assumed
to initially evolve in a sine-Gordon potential with velocity $v$ and
oscillation frequency $\omega$. We then consider two types of numerical
experiments: a. An abrupt transition of the potential to a $\Phi^4$ form at
t_0=0 over the whole 1-dimensional lattice and b. The impact of the breather on
a region x>x_0=0 where the potential has the \Phi^4 form which is different
from the sine-Gordon form valid at x<x_0=0. We find that in both cases there is
a region of parameters (v,\omega) such that the breather decays to a
kink-antikink pair. This region of parameters for kink-antikink formation is
qualitatively similar with the parameter region where the energy of the
breather exceeds the energy of the kink-antikink pair in the \Phi^4 potential.
We demonstrate that the same mechanism for soliton formation is realized when
using a gaussian oscillator (oscillon) instead of a breather. We briefly
discuss the implications of our results for realistic experiments as well as
their extension to soliton formation in two and three space dimensions.
