Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Parametric pumping and kinetics of magnons in dipolar ferromagnets   The time evolution of magnons subject to a time-dependent microwave field is
usually described within the so-called "S-theory", where kinetic equations for
the distribution function are obtained within the time-dependent Hartree-Fock
approximation. To explain the recent observation of "Bose-Einstein condensation
of magnons" in an external microwave field [Demokritov et al., Nature 443, 430
(2006)], we extend the "S-theory" to include the Gross-Pitaevskii equation for
the time-dependent expectation values of the magnon creation and annihilation
operators. We explicitly solve the resulting coupled equations within a simple
approximation where only a single condensed mode is retained. We also
re-examine the usual derivation of an effective boson model from a realistic
spin model for yttrium-iron garnet films and argue that in the parallel pumping
geometry (where both the static and the time-dependent magnetic field are
parallel to the macroscopic magnetization) the time-dependent Zeemann energy
cannot give rise to magnon condensation.

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The categories of this paper are: bayes-an
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The categories of this paper are: q-alg
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The categories of this paper are: comp-gas
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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: chem-ph
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The categories of this paper are: solv-int
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The categories of this paper are: nucl-th
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The categories of this paper are: eess
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The categories of this paper are: alg-geom
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The categories of this paper are: supr-con
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The categories of this paper are: mtrl-th
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The categories of this paper are: dg-ga
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The categories of this paper are: acc-phys
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The categories of this paper are: econ
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The categories of this paper are: funct-an