Stretched-exponential relaxation in arrays of coupled rotators

We consider the non-equilibrium dynamics of a chain of classical rotators coupled at its edges to an external reservoir at zerotemperature. We find that the energy is released in a strongly discontinuous fashion, with sudden jumps alternated with longstretches during which dissipation is extremely weak. The jumps mark the disappearance of strongly localized structures, akinto the rotobreather solutions of the Hamiltonian model, which act as insulating boundaries of a hot central core. As a result ofthis complex kinetics, the ensemble-averaged energy follows a stretched exponential law until a residual pseudo-stationary stateis attained, where the hot core has reduced to a single localized object.We give a statistical description of the relaxation pathway and connect it to the properties of return periods of rare events incorrelated time series. This approach sheds some light into the microscopic mechanism underlying the slow dynamics of thesystem.Finally, we show that the stretched exponential law remains unaltered in the presence of isotopic disorder.