Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Is the NANOGrav signal a hint of dS decay during inflation?   As suggested by the swampland conjectures, de Sitter (dS) space might be
highly unstable if it exists at all. During inflation, the short-lived dS
states will decay through a cascade of the first-order phase transition (PT).
We find that the gravitational waves (GWs) yielded by such a PT will be
"reddened" by subsequent dS expansion, which may result in a slightly red-tilt
stochastic GWs background at low-frequency band, compatible with the NANOGrav
12.5-yr result.

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The categories of this paper are: atom-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: math
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The categories of this paper are: supr-con
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The categories of this paper are: chem-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: adap-org
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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: nucl-th
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The categories of this paper are: chao-dyn
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The categories of this paper are: eess
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The categories of this paper are: hep-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: q-bio
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The categories of this paper are: quant-ph