Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Effect of broken symmetry on resonant inelastic x-ray scattering from
  undoped cuprates   We study the magnetic excitation spectra of resonant inelastic x-ray
scattering (RIXS) at the $L$-edge from undoped cuprates beyond the fast
collision approximation. We analyse the effect of the symmetry breaking ground
state on the RIXS process of the Heisenberg model by using a projection
procedure. We derive the expressions of the scattering amplitude in both
one-magnon and two-magnon excitation channels. Each of them consists of the
isotropic and anisotropic contributions. The latter is a new finding and
attributed to the long range order of the ground state. The presence of
anisotropic terms is supported by numerical calculations on a two-dimensional
spin cluster. We express the RIXS spectra in the form of spin-correlation
functions with the coefficients evaluated on the cluster, and calculate the
function in a two dimensional system within the $1/S$ expansion. Due to the
anisotropic terms, the spectral intensities are considerably enhanced around
momentum transfer $\textbf{q}=0$ in both one-magnon and two-magnon excitation
channels. This finding may be experimentally confirmed by examining carefully
the $\textbf{q}$-dependence of the spectra.

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The categories of this paper are: adap-org
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The categories of this paper are: comp-gas
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The categories of this paper are: nucl-th
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The categories of this paper are: math
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The categories of this paper are: cs
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The categories of this paper are: dg-ga
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The categories of this paper are: hep-th
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The categories of this paper are: patt-sol
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The categories of this paper are: q-alg
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The categories of this paper are: hep-lat
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The categories of this paper are: physics
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The categories of this paper are: bayes-an
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The categories of this paper are: quant-ph
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The categories of this paper are: econ
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The categories of this paper are: funct-an
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The categories of this paper are: gr-qc