Thermalization without chaos in harmonic systems

Recent numerical results showed that thermalization of Fourier modes is achieved in short time-scales in the Toda model, despite its integrability and the absence of chaos. Here we provide numerical evidence that the scenario according to which chaos is irrelevant for thermalization is realized even in the simplest of all classical integrable system: the harmonic chain. We study relaxation from an atypical condition given with respect to random modes, showing that a thermal state with equilibrium properties is attained in short times. Such a result is independent from the orthonormal basis used to represent the chain state, provided it is a random basis.