Evidence for the nonlinear transport of galactic cosmic rays

The measured decrease of the abundance ratio of secondary to primary Galactic cosmic- ray nuclei is explained by the increase of the cosmic- ray parallel mean free path with magnetic rigidity lambda(vertical bar vertical bar) proportional to R-0.6 that results from the weakly nonlinear transport theory of cosmic rays in the turbulent Galactic magnetic fields. Because the ratio of fluctuating to ordered magnetic fields in the Galaxy q(L) = (delta B/B-0)(2) is large, this nonlinear transport theory has to be favored over the traditional quasi- linear theory that requires very small values q(L) << 1. Our explanation provides an alternative to Galactic transport theories of cosmic rays with significant distributed stochastic acceleration.