Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Magnon-induced long-range correlations and their neutron-scattering
  signature in quantum magnets   We consider the coupling of the magnons in both quantum ferromagnets and
antiferromagnets to the longitudinal order-parameter fluctuations, and the
resulting nonanalytic behavior of the longitudinal susceptibility. In classical
magnets it is well known that long-range correlations induced by the magnons
lead to a singular wave-number dependence of the form $1/k^{4-d}$ in all
dimensions 2<d<4, for both ferromagnets and antiferromagnets. At zero
temperature we find a profound difference between the two cases. Consistent
with naive power counting, the longitudinal susceptibility in a quantum
antiferromagnet scales as $k^{d-3}$ for 1<d<3, whereas in a quantum ferromagnet
the analogous result, $k^{d-2}$, is absent due to a zero scaling function. This
absence of a nonanalyticity in the longitudinal susceptibility is due to the
lack of magnon number fluctuations in the ground state of a quantum
ferromagnet; correlation functions that are sensitive to other fluctuations do
exhibit the behavior predicted by simple power counting. Also of interest is
the dynamical behavior as expressed in the longitudinal part of the dynamical
structure factor, which is directly measurable via neutron scattering. For both
ferromagnets and antiferromagnets there is a logarithmic singularity at the
magnon frequency with a prefactor that vanishes as $T\to 0$. In the
antiferromagnetic case there also is a nonzero contribution at T=0 that is
missing for ferromagnets. Magnon damping due to quenched disorder restores the
expected scaling behavior of the longitudinal susceptibility in the
ferromagnetic case; it scales as $k^{d-2}$ if the order parameter is not
conserved, or as $k^d$ if it is. Detailed predictions are made for both two-
and three-dimensional systems at both T=0 and in the limit of low temperatures,
and the physics behind the various nonanalytic behaviors is discussed.

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The categories of this paper are: astro-ph
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The categories of this paper are: econ
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The categories of this paper are: acc-phys
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The categories of this paper are: hep-lat
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The categories of this paper are: quant-ph
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The categories of this paper are: plasm-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: stat
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The categories of this paper are: gr-qc
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The categories of this paper are: comp-gas
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The categories of this paper are: bayes-an
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The categories of this paper are: cs
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The categories of this paper are: cmp-lg
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The categories of this paper are: patt-sol
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The categories of this paper are: q-bio
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The categories of this paper are: eess