  We investigate the role that quasinormal modes can play in kink-antikink
collisions, via an example based on a perturbation of the $\phi^4$ model. We
find that narrow quasinormal modes can store energy during collision processes
and return it back to the translational degrees of freedom. Quasinormal modes
also decay, which leads to energy leakage, causing a closing of resonance
windows and an increase of the critical velocity. We observe similar phenomena
in an effective model, a small modification of the collective-coordinate
approach to the $\phi^4$ model.

High Energy Physics - Theory