Deviation from fluctuation-dissipation relation for driven superdiffusion: Polymer stretching as an example

We discuss a deviation of the fluctuation-dissipation relation (FDR) in a driven superdiffusive system as exemplified by polymer stretching. The superdiffusion is found by monitoring momentum transfer to a tracer, which is a conjugate observable with the position. Molecular-dynamics simulation demonstrates that the FDR deviates during the nonequilibrium transient process. We then propose nonequilibrium mode analysis for superdiffusion, which is a counterpart to that for driven subdiffusion. The mode analysis yields results that are in qualitative agreement with the simulation results, suggesting that the fluctuations of the stiffness in the system from initial equilibrium to stretching account for the FDR deviation.