Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Gauge couplings in four-dimensional Type I string orbifolds   We compute threshold effects to gauge couplings in four-dimensional $Z_N$
orientifold models of type I strings with ${\cal N}=2$ and ${\cal N}=1$
supersymmetry, and study their dependence on the geometric moduli. We also
compute the tree-level (disk) couplings of the open sector gauge fields to the
twisted closed string moduli of the orbifold in various models and study their
effects and that of the one-loop threshold corrections on gauge coupling
unification. We interpret the results from the (supergravity) effective theory
point of view and comment on the conjectured heterotic-type I duality

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The categories of this paper are: dg-ga
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The categories of this paper are: solv-int
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The categories of this paper are: chao-dyn
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The categories of this paper are: cond-mat
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The categories of this paper are: nucl-ex
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The categories of this paper are: comp-gas
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The categories of this paper are: mtrl-th
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The categories of this paper are: hep-ex
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The categories of this paper are: q-bio
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The categories of this paper are: econ
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The categories of this paper are: chem-ph
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The categories of this paper are: physics
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The categories of this paper are: math
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The categories of this paper are: gr-qc
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The categories of this paper are: quant-ph
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The categories of this paper are: math-ph