Polarization analysis of gravitational-wave backgrounds from the correlation signals of ground-based interferometers: Measuring a circular-polarization mode

The Stokes V parameter characterizes asymmetry of amplitudes between right- and left-handed waves, and the nonvanishing value of the V parameter yields a circularly polarized signal. Cosmologically, the V parameter may be a direct probe for parity violation in the Universe. In this paper, we theoretically investigate a measurement of this parameter, particularly focusing on the gravitational-wave backgrounds observed via ground-based interferometers. In contrast to the traditional analysis that only considers the total amplitude (or equivalently ΩGW), the signal analysis including a circular-polarized mode has a rich structure due to the multidimensionality of target parameters. We show that, by using the network of next-generation detectors, separation between polarized and unpolarized modes can be performed with small statistical loss induced by their correlation.