Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Parametric decay of parallel and oblique Alfven waves in the expanding
  solar wind   The long-term evolution of large-amplitude Alfven waves propagating in the
solar wind is investigated by performing two-dimensional MHD simulations within
the expanding box model. The linear and nonlinear phases of the parametric
decay instability are studied for both circularly polarized waves in parallel
propagation and for arc-polarized waves in oblique propagation. The
non-monochromatic case is also considered. In the oblique case, the direct
excitation of daughter modes transverse to the local background field is found
for the first time in an expanding environment, and this transverse cascade
seems to be favored for monochromatic mother waves. The expansion effect
reduces the instability growth rate, and it can even suppress its onset for the
lowest frequency modes considered here, possibly explaining the persistence of
these outgoing waves in the solar wind.

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The categories of this paper are: gr-qc
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The categories of this paper are: quant-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: supr-con
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The categories of this paper are: comp-gas
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The categories of this paper are: q-fin
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The categories of this paper are: patt-sol
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The categories of this paper are: hep-ex
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The categories of this paper are: econ
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The categories of this paper are: nucl-ex
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The categories of this paper are: adap-org
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The categories of this paper are: q-alg
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The categories of this paper are: dg-ga
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The categories of this paper are: chem-ph
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The categories of this paper are: math
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The categories of this paper are: eess