Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Worldsheet instantons and coupling selection rules in heterotic
  orbifolds   We review recent results on string coupling selection rules for heterotic
orbifolds, derived using conformal field theory. Such rules are the first step
towards understanding the viability of the recently obtained compactifications
with potentially realistic particle spectra. They arise from the properties of
the worldsheet instantons that mediate the couplings, and include stringy
effects that would seem 'miraculous' to an effective field theory observer.

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The categories of this paper are: bayes-an
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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-fin
0
The categories of this paper are: hep-ph
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The categories of this paper are: math-ph
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The categories of this paper are: solv-int
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The categories of this paper are: gr-qc
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The categories of this paper are: hep-lat
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The categories of this paper are: plasm-ph
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The categories of this paper are: math
1
The categories of this paper are: cs
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The categories of this paper are: adap-org
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The categories of this paper are: chao-dyn
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The categories of this paper are: ao-sci
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The categories of this paper are: funct-an