Kink-Antikink Collisions in the Two-Dimensional  4 Model

Inelastic kink-antikink collisions are investigated in the two-dimensional φ4 model. It is shown that a bound state of the kink and antikink is formed when the colliding velocity V is less than a critical Vc, and that inelastic scattering of the kinks is caused when V>Vc. These phenomena are due to the excitation of internal modes of the kinks. An excited kink is not stable but emits bosons to decay into the ground state kink. Numerical calculations were also performed for classical kink-anitikink collision processes.