Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Dark Radiation and the Hagedorn Phase   We point out that if the sector associated with the Standard Model degrees of
freedom entered an open string Hagedorn phase in the early universe while the
dark radiation sector was not part of this plasma, then this can lead to low
values of the observable $\Delta N_{\text{eff}}$ (number of additional
neutrino-like species) from the dark radiation. For explicit analysis, we focus
on warped string compactifications with the Standard Model degrees of freedom
at the bottom of a warped throat. If the Hubble scale during inflation is above
the warped string scale associated with the throat, then the Standard Model
sector will enter the Hagedorn phase. In this scenario, bulk axions are no
longer dangerous from the point of view of dark radiation. While this article
focuses on warped compactifications, the basic idea can be relevant to any
scenario where the early universe entered a Hagedorn phase.

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The categories of this paper are: hep-ex
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The categories of this paper are: q-alg
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The categories of this paper are: nlin
35
The categories of this paper are: mtrl-th
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The categories of this paper are: atom-ph
2
The categories of this paper are: math
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The categories of this paper are: nucl-th
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The categories of this paper are: adap-org
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The categories of this paper are: eess
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The categories of this paper are: quant-ph
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The categories of this paper are: funct-an
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The categories of this paper are: ao-sci
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The categories of this paper are: supr-con
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The categories of this paper are: physics
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The categories of this paper are: chem-ph
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The categories of this paper are: comp-gas