Year: 2026
Type: article
Abstract: Recent Pulsar Timing Array datasets provide compelling evidence for a nano-Hertz gravitational-wave background, but robust detection requires characterizing statistical fluctuations of the Hellings-Downs (HD) correlation expected from a finite population of discrete sources. Building on the variance calculation of Allen (2023), we derive the third central moment (skewness) of the HD correlation for a single unpolarized point source and an ensemble of many interfering point sources in the confusion-noise regime. To isolate the intrinsic non-Gaussianity of the background, we extend the pulsar-averaging formalism to third order by introducing a three-point averaged correlation function, which allows us to define the cosmic skewness. We find that the skewness remains non-zero in the large-source-number limit and is controlled by a new geometric three-point function. These results suggest that incorporating higher-order moments could provide additional information on source discreteness beyond standard Gaussian analyses.
Authors: Fujimoto, Ryosuke, Takahashi, Keitaro
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Awards: G2403003013, Exploratory Study on the Detection of the 21cm Global Signal of Neutral Hydrogen, Investigating the first star formation and reionization process of the Universe by MWA, Frontiers of Cosmic Reionization and Galaxy Formation Opened Up by the Massive Spectroscopic Survey with Subaru PFS, G6499107354, G7400142624
OpenAlex ID: W7127366351
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