Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Cosmic-ray acceleration at collisionless astrophysical shocks using
  Monte-Carlo simulations   Context. The diffusive shock acceleration mechanism has been widely accepted
as the acceleration mechanism for galactic cosmic rays. While self-consistent
hybrid simulations have shown how power-law spectra are produced, detailed
information on the interplay of diffusive particle motion and the turbulent
electromagnetic fields responsible for repeated shock crossings are still
elusive. Aims. The framework of test-particle theory is applied to investigate
the effect of diffusive shock acceleration by inspecting the obtained
cosmic-ray energy spectra. The resulting energy spectra can be obtained this
way from the particle motion and, depending on the prescribed turbulence model,
the influence of stochastic acceleration through plasma waves can be studied.
Methods. A numerical Monte-Carlo simulation code is extended to include
collisionless shock waves. This allows one to trace the trajectories of test
particle while they are being accelerated. In addition, the diffusion
coefficients can be obtained directly from the particle motion, which allows
for a detailed understanding of the acceleration process. Results. The classic
result of an energy spectrum with $E^{-2}$ is only reproduced for parallel
shocks, while, for all other cases, the energy spectral index is reduced
depending on the shock obliqueness. Qualitatively, this can be explained in
terms of the diffusion coefficients in the directions that are parallel and
perpendicular to the shock front.

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The categories of this paper are: bayes-an
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The categories of this paper are: dg-ga
31
The categories of this paper are: ao-sci
5
The categories of this paper are: gr-qc
29
The categories of this paper are: funct-an
15
The categories of this paper are: nucl-ex
10
The categories of this paper are: q-bio
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The categories of this paper are: plasm-ph
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The categories of this paper are: solv-int
0
The categories of this paper are: hep-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: nlin
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The categories of this paper are: chao-dyn
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The categories of this paper are: chem-ph
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The categories of this paper are: q-fin
2
The categories of this paper are: math