Intermittent many-body dynamics at equilibrium

Abstract

The equilibrium value of an observable denes a manifold in the phase space of an ergodic and equipartitioned many-body system. A typical trajectory pierces that manifold innitely often as time goes to innity. We use these piercings to measure both the relaxation time of the lowest frequency eigenmode of the Fermi-Pasta-Ulam chain (FPU), as well as the uctuations of the subsequent dynamics in equilibrium. The dynamics in equilibrium is characterized by a power-law distribution of excursion times far o equilibrium, with diverging variance. Long excursions arise from sticky dynamics close to q-breathers localized in normal mode space. Measuring the exponent allows to predict the transition into nonergodic dynamics. We generalize our method to Klein-Gordon lattices (KG) where the sticky dynamics is due to discrete breathers localized in real space. (c) 2017 American Physical Society