SOLITON-LIKE BEHAVIOR IN A MODIFIED SINE-GORDON MODEL

We consider a sine-Gordon model in 1 + 1 dimensions modified by the ad dition of a further kinetic term similar to the Skyrme term in higher dimensions and an extra potential term. The model has interesting prop erties. In particular, in addition to the familiar sine-Gordon soliton it possesses a double-kink solution which has an internal oscillatory mode. The sine-Gordon kink has a definite velocity and this velocity is a critical velocity for the double-kink structures. For some range of the parameters the model has two different solutions, with the same boundary conditions, which propagate at the velocity of the sine-Gord on kink. When the exact solutions are perturbed or acted upon by an ex ternal force they radiate short wavelength oscillations and keep a vel ocity which remains below the critical value. The same radiation can a lso stabilize the speed of pi-kink solutions for which the boundary co nditions correspond to two different levels of the potential energy.