Relativistic trajectory variables in 1+1 dimensional Ruijsenaars-Schneider type models

A general algorithm to construct particle trajectories in 1+1 dimensional canonical relativistic models is presented. The method is a generalization of the construction used in Ruijsenaars-Schneider models and provides a simple proof of the fact that the latter satisfies the world-line conditions granting proper physical Poincare invariance. The 2-particle case for the rational Ruijsenaars-Schneider model is worked out explicitly. It is shown that the particle coordinates do not Poisson commute, as required by the no-interaction theorem of Currie, Jordan and Sudarshan.