Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Cosmic Ray Transport with Magnetic Focusing and the "Telegraph" model   Cosmic rays (CR), constrained by scattering on magnetic irregularities, are
believed to propagate diffusively. But a well-known defect of diffusive
approximation whereby some of the particles propagate unrealistically fast has
directed interest towards an alternative CR transport model based on the
"telegraph" equation. However, its derivations often lack rigor and
transparency leading to inconsistent results.
  We apply the classic Chapman-Enskog method to the CR transport problem. We
show that no "telegraph" (second order time derivative) term emerges in any
order of a proper asymptotic expansion with systematically eliminated short
time scales. Nevertheless, this term may formally be\emph{ converted} from the
\emph{fourth} order hyper-diffusive term of the expansion. But, both the
telegraph and hyperdiffusive terms may only be important for a short relaxation
period associated with either strong pitch-angle anisotropy or spatial
inhomogeneity of the initial CR distribution. Beyond this period the system
evolves diffusively in both cases. The term conversion, that makes the
telegraph and Chapman-Enskog approaches reasonably equivalent, is possible only
after this relaxation period. During this period, the telegraph solution is
argued to be unphysical. Unlike the hyperdiffusion correction, it is not
uniformly valid and introduces implausible singular components to the solution.
These dominate the solution during the relaxation period. As they are shown not
to be inherent in the underlying scattering problem, we argue that the
telegraph term is involuntarily acquired in an asymptotic reduction of the
problem.

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The categories of this paper are: chem-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: hep-th
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The categories of this paper are: plasm-ph
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The categories of this paper are: solv-int
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The categories of this paper are: ao-sci
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The categories of this paper are: mtrl-th
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The categories of this paper are: cs
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The categories of this paper are: acc-phys
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The categories of this paper are: eess
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The categories of this paper are: q-fin
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The categories of this paper are: atom-ph
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The categories of this paper are: cond-mat
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The categories of this paper are: q-bio
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The categories of this paper are: chao-dyn
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The categories of this paper are: alg-geom