Diffusive shock acceleration: non-classical model of cosmic ray transport

Abstract

In this work the theory of diffusive shock acceleration is extended to the case of non-classical particle transport with L\'{e}vy flights and L\'{e}vy traps, when the mean square displacement grows nonlinearly with time. In this approach the Green function is not a Gaussian but it exhibits power-law tails. By using the propagator appropriate for non-classical diffusion, it is found for the first time that energy spectral index of particles accelerated at shock front is $\gamma = [\alpha (\mathrm{r} + 5) - 6 \beta]/[\alpha(\mathrm{r}-1)]$, where $0 < \alpha < 2$ and $0 <\beta < 1$ are the exponents of power-law behavior of L\'{e}vy flights and L\'{e}vy traps, respectively. We note that this result coincides with standard slope at $\alpha=2, \beta=1$ (normal diffusion), and also includes those obtained earlier for the subdiffusion ($\alpha=2, \beta<1$) and superdiffusion ($\alpha<2, \beta=1$) regimes.