title: Breather-breather interactions in sine-Gordon systems using collective coordinate approach.
abstract: We investigate the interaction between breathers in sine-Gordon systems using a collective coordinate approach. Focusing on the in-phase or out-of-phase oscillation mode of two identical breathers, we derive a simple ordinary differential equation for the collective coordinate: the separation between the centers of mass of the two breathers R. Analytic solutions of this equation can reproduce quantitatively the results of a direct numerical simulation of the sine-Gordon equation over the whole parameter range. The interaction between the two breathers is attractive (repulsive) for the in-phase (out-of-phase) oscillation mode with an asymptotic exponential dependence on R. We find that the interaction within the innermost kink-antikink (kink-kink) pair for the in-phase (out-of-phase) case plays the most significant role in determining the sign and the strength of the effective breather-breather interaction. We also find an internal oscillation mode of the in-phase oscillating breather pair and obtain an analytic expression for the angular frequency of the mode.
authors.affiliation: Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashi-Hiroshima 739-8530, Japan.
authors.forename: Munehiro
authors.initials: M
authors.lastname: Nishida
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Furukawa
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Fujii
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Hatakenaka
mesh_terms: D003198:Computer Simulation; D008962:Models, Theoretical; D017711:Nonlinear Dynamics; D009991:Oscillometry / Q000379:methods*