Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Potential dangers when phase shifts are used as a link between
  experiment and QCD   Luscher has shown that in single channel problem (elastic region below first
inelastic threshold) there exists a direct link between the discrete value of
the energy in a finite QCD volume and the scattering phase shift at the same
energy. However, when the extension of the theorem is made to the baryon
resonance sector (multi-channel situation in the inelastic region above first
inelastic threshold), eigenphases (diagonal multi-channel quantities) replace
phase shifts (single channel quantities). It is necessary to stress that the
renowned pi/2 resonance criterion is formulated for eigenphases and not for
phase shifts, so the resonance extracting procedure has to be applied with
utmost care. The potential instability of extracting eigenphases from
experimental data which occurs if insufficient number of channels is used can
be reduced if a trace function which explicitly takes multi-channel aspect of
the problem into account is used instead of single-channel phase shifts.

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The categories of this paper are: math
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The categories of this paper are: atom-ph
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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: adap-org
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The categories of this paper are: solv-int
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The categories of this paper are: hep-lat
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The categories of this paper are: chao-dyn
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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: cmp-lg
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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: nucl-ex
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The categories of this paper are: q-alg
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The categories of this paper are: math-ph