Characterize the role of magnetic-field-line subdiffusion

Characterize whether subdiffusion of magnetic field lines contributes to the anomalous energy dependence of the perpendicular diffusion coefficient, in addition to stochastic gradient and curvature drifts, particularly at low turbulence levels.

Background

The paper proposes that stochastic gradient and curvature drifts, especially those associated with the turbulent magnetic-field component parallel to the guide field, explain the increase of the ratio of perpendicular to parallel diffusion with particle energy. Earlier work attributed the behavior partly to a subdiffusive phase in magnetic-field-line random walk.

The simulations in this paper do not show a clear subdiffusive signature for turbulence levels near unity, but the authors note that subdiffusion could still contribute when the turbulence amplitude is lower. Its quantitative role relative to stochastic drifts therefore remains unresolved.

References

However, we cannot exclude that the subdiffusion of magnetic field lines, discussed by , may also play a role, especially for low values of $\zeta$.

— Perpendicular transport in isotropic magnetic turbulence. The role of stochastic drifts  (2610.13865 - Pucci et al., 9 Oct 2026) in Section 6, “Conclusions”