Universality classes of transition fronts in the FPU model
Résumé
Steady transition fronts in nonlinear lattices are among the most important dynamic coherent structures. We use the Fermi-Pasta-Ulam model with piecewise linear nonlinearity to show that there are exactly three distinct classes of such fronts which differ fundamentally in how (and whether) they produce and transport oscillations. To make this Hamiltonian problem analytically transparent, we construct a quasicontinuum approximation generating all three types of fronts and then show that the interconnection between different classes of fronts in the original discrete model is the same as in the quasicontinuum model. The proposed framework unifies previous attempts to classify the transition fronts as radiative, dispersive, topological or compressive and categorizes them instead as different types of dynamic defects.
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