Different effects of external force fields on aging Lévy walk

Abstract

Aging phenomena have been observed in numerous physical systems. Many statistical quantities depend on the aging time $t_a$ for aging anomalous diffusion processes. This paper pays more attention to how an external force field affects the aging Lévy walk. Based on the Langevin picture of Lévy walk and generalized Green-Kubo formula, we investigate the quantities which include the ensemble- and time-averaged mean-squared displacements in both weak aging $t_a\ll t$ and strong aging $t_a\gg t$ cases, and compare them to the quantities in the absence of any force field. Two typical force fields, constant force $F$ and time-dependent periodic force $F(t)=f_0\sin (\omega t)$, are considered for comparison. The generalized Einstein relation is also discussed in the case with constant force. We find that the constant force is the key of generating the aging phenomena and enhancing the diffusion behavior of aging Lévy walk, while the time-dependent periodic force is not. The different effects of the two kinds of forces on the aging phenomena of Lévy walk are verified by both theoretical analyses and numerical simulations.