Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spinor-Vector Duality in Heterotic String Orbifolds   The three generation heterotic-string models in the free fermionic
formulation are among the most realistic string vacua constructed to date,
which motivated their detailed investigation. The classification of free
fermion heterotic string vacua has revealed a duality under the exchange of
spinor and vector representations of the SO(10) GUT symmetry over the space of
models. We demonstrate the existence of the spinor-vector duality using
orbifold techniques, and elaborate on the relation of these vacua to free
fermionic models.

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The categories of this paper are: q-bio
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The categories of this paper are: nlin
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The categories of this paper are: funct-an
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The categories of this paper are: cs
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The categories of this paper are: gr-qc
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The categories of this paper are: q-fin
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The categories of this paper are: bayes-an
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The categories of this paper are: hep-lat
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The categories of this paper are: eess
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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: chem-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: acc-phys
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The categories of this paper are: adap-org
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The categories of this paper are: plasm-ph