Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Threshold singularities in the XXZ- spin chain   We calculate the critical exponents of the threshold singularity for the
spectral density of the XXZ- spin chain at zero magnetic field for the lower
threshold. We show that the corresponding phase shifts are momentum-independent
and coinside with the predictions of the effective mobile impurity Hamiltonian
approach. We show that for the eigenstates with the high-energy particle with
the momentum $k$ which is much larger than the momenta of the particle-hole
excitations the formfactor is not described in the framework of the Luttinger
model even in the limit $k<<p_F$ but should be evaluated in the framework of
the effective mobile impurity Hamiltonian approach.

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The categories of this paper are: atom-ph
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The categories of this paper are: astro-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: q-fin
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The categories of this paper are: funct-an
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The categories of this paper are: stat
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The categories of this paper are: cmp-lg
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The categories of this paper are: ao-sci
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The categories of this paper are: hep-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: nucl-th
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The categories of this paper are: physics
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The categories of this paper are: adap-org
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The categories of this paper are: quant-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: q-alg