A DUMBBELLS RANDOM-WALK IN CONTINUOUS-TIME

We study the continuous-time dynamics of a rigid dumbbell or, equivale ntly, of two random walkers coupled through a holonomic constraint. Ra ndom walkers under holonomic constraints provide a generic model for m any physical systems, e.g. for polymers. Interestingly, the spatial an d temporal aspects of the dumbbell's motion are highly coupled: the en suing behaviour differs considerably from a simple continuous-time ran dom walk (CTRW)-picture. For waiting-time distributions with broad pro bability densities the dumbbell's dynamics parallels that of polymers in melts, in that two diffusive regimes appear, connected by a broad c rossover region. We determine analytically the diffusion constants in the two regimes from a higher-order decoupling approach; the results a gree well with simulations.