Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Cosmic-Ray Proton to Electron Ratios   A basic quantity in the characterization of relativistic particles is the
proton-to-electron (p/e) energy density ratio. We derive a simple approximate
expression suitable to estimate this quantity, U_p/U_e = (m_p/m_e)^(3-q)/2,
valid when a nonthermal `gas' of these particles is electrically neutral and
the particles' power-law spectral indices are equal -- e.g., at injection. This
relation partners the well-known p/e number density ratio at 1 GeV, i.e.
N_p/N_e = (m_p/m_e)^{(q-1)/2}.

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The categories of this paper are: cs
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The categories of this paper are: q-fin
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The categories of this paper are: chao-dyn
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The categories of this paper are: math-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: nucl-ex
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The categories of this paper are: physics
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The categories of this paper are: cond-mat
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The categories of this paper are: chem-ph
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The categories of this paper are: eess
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The categories of this paper are: comp-gas
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The categories of this paper are: patt-sol
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The categories of this paper are: dg-ga
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The categories of this paper are: plasm-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: quant-ph