Circular Polarization of the Astrophysical Gravitational Wave Background

Abstract

The circular polarization of gravitational waves is a powerful observable to test parity violation in gravity and to distinguish between the primordial or the astrophysical origin of the stochastic background. This property comes from the expected unpolarized nature of the homogeneous and isotropic astrophysical background, contrary to some specific cosmological sources that can produce a polarized background. However, in this work we show that there is a non-negligible amount of circular polarization also in the astrophysical background, generated by Poisson fluctuations in the number of unresolved sources, which can be detected by the third-generation interferometers with signal-to-noise ratio larger than one. We also explain in which cases the gravitational wave maps can be cleaned from this extra source of noise, exploiting the frequency and the angular dependence, in order to search for signals from the early Universe. Future studies about the detection of polarized cosmological backgrounds with ground- and space-based interferometers should account for the presence of such a foreground contribution.

10 pages, 1 figure. V2 matches the version accepted by PRL for publication

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• Anisotropies in Scalar-Induced Gravitational-Wave Background from Inflaton-Curvaton Mixed Scenario with Sound Speed Resonance
• On the anisotropies of the cosmological gravitational-wave background from pulsar timing array observations
• First astrometric constraints on parity-violation in the gravitational wave background
• Estimating the gravitational wave background anisotropy: a Bayesian approach boosted by cross-correlation angular power spectrum