Kink-antikink interactions in a modified sine-Gordon model

We study numerically the interactions of a kink (K) and an antikink (anti K) in a parametrically modified sine-Gordon model with potential V(PHI)=(1-r)2(1-cos PHI)/(1+r2+2r cos PHI). As the parameter r is varied from the pure sine-Gordon case (r=0) to values for which the model is not completely integrable (rnot=0), we find that a rich structure arises in the Kanti K collisions. For some regions of r(-0.20< or approx.r<0) this structure is very similar to that observed in Kanti K interactions in the PHI4 model, and we show that the theory recently suggested for these collisions also applies quantitatively to the modified sine-Gordon model. In other regions of r we observe new scattering phenomena, which we present in detail numerically and discuss in a qualitative manner analytically. (orig.)