π-kinks in the parametrically driven sine-Gordon equation and applications

Parametrically driven sine-Gordon equation with a mean-zero forcing is considered. It is shown that the system is well approximated by the double sine-Gordon equation using the normal form technique. The reduced equation possesses π-kink solutions, which are also observed numerically in the original system. This result is applied to domain walls dynamics in one-dimensional easy-plane ferromagnets. For such system the existence of π-kinks implies the "true" domain structure in the presence of high-frequency magnetic field.