COSMIC-RAY STREAMING IN THE BORN APPROXIMATION

Previous studies of the effect of magnetic helicity on cosmic-ray transport agree that helicity modifies both the parallel diffusion coefficient and the convection speed in a manner dependent upon particle charge sign, but they disagree as to the magnitude and even the direction of the effect. The present work invokes the Born approximation to derive a more accurate expression for the streaming of cosmic rays parallel to the mean magnetic field. While all prior results pertaining to the helicity dependence of the diffusion coefficient and convection speed can be recovered as special cases from this streaming equation, we conclude that a new set of transport parameters presented here is more appropriate for the solar modulation of galactic cosmic rays. In addition, we introduce a new parameter related to time variability, which may be a dominant cause of charge sign-dependent transport of solar particles.