Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Can the Axions of Standard--like Superstring Models Solve the Strong CP
  Problem?   We find that there are three axions in standard--like superstring models in
the four dimensional free fermionic formulation. These axions are either
harmful or very heavy. Therefore, they cannot solve the strong CP problem. We
show that this is a general result in superstring models with chiral
generations from the $Z_2$ twisted sectors which use a $Z_4$ twist.

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The categories of this paper are: astro-ph
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The categories of this paper are: quant-ph
15
The categories of this paper are: nucl-ex
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The categories of this paper are: funct-an
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The categories of this paper are: hep-ex
9
The categories of this paper are: nlin
3
The categories of this paper are: physics
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The categories of this paper are: dg-ga
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The categories of this paper are: stat
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The categories of this paper are: supr-con
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The categories of this paper are: q-bio
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The categories of this paper are: chao-dyn
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The categories of this paper are: comp-gas
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The categories of this paper are: eess
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The categories of this paper are: hep-lat
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The categories of this paper are: econ