title: Instabilities and relaxation to equilibrium in long-range oscillator chains.
abstract: We study instabilities and relaxation to equilibrium in a long-range extension of the Fermi-Pasta-Ulam-Tsingou (FPU) oscillator chain by exciting initially the lowest Fourier mode. Localization in mode space is stronger for the long-range FPU model. This allows us to uncover the sporadic nature of instabilities, i.e., by varying initially the excitation amplitude of the lowest mode, which is the control parameter, instabilities occur in narrow amplitude intervals. Only for sufficiently large values of the amplitude, the system enters a permanently unstable regime. These findings also clarify the long-standing problem of the relaxation to equilibrium in the short-range FPU model. Because of the weaker localization in mode space of this latter model, the transfer of energy is retarded and relaxation occurs on a much longer timescale.
authors: Department of Physics, Faculty of Exact and Natural Sciences, Tbilisi State University, 0128 Tbilisi, Georgia.|Department of Physics, The University of Texas at Austin, Austin TX 78712, USA.
authors: George
authors: G
authors: Miloshevich
authors: Fundamental Physics Laboratory: Group of Nonlinear Physics and Complex Systems, Department of Physics, University of Douala, P.O. Box 24157, Douala, Cameroon.|Laboratoire de Physique de l'ENS Lyon, Université de Lyon, CNRS, 46, allée d'Italie, 69007 Lyon, France.
authors: Jean-Pierre
authors: JP
authors: Nguenang
authors: Laboratoire de Physique de l'ENS Lyon, Université de Lyon, CNRS, 46, allée d'Italie, 69007 Lyon, France.
authors: Thierry
authors: T
authors: Dauxois
authors: Department of Physics, Faculty of Exact and Natural Sciences, Tbilisi State University, 0128 Tbilisi, Georgia.|Dipartimento di Fisica e Astronomia and CSDC, Università di Firenze, CNISM and INFN, via G. Sansone, 1, Sesto Fiorentino, Italy.
authors: Ramaz
authors: R
authors: Khomeriki
authors: Dipartimento di Fisica e Astronomia and CSDC, Università di Firenze, CNISM and INFN, via G. Sansone, 1, Sesto Fiorentino, Italy.
authors: Stefano
authors: S
authors: Ruffo