Prospects for direct detection of circular polarization of gravitational-wave background

We discussed prospects for directly detecting circular polarization signal of gravitational wave background. We found it is generally difficult to probe the monopole mode of the signal due to broad directivity of gravitational wave detectors. But the dipole (l = 1) and octupole (l = 3) modes of the signal can be measured in a simple manner by combining outputs of two unaligned detectors, and we can dig them deeply under confusion and detector noises. Around f ∼ 0.1mHz LISA will provide ideal data streams to detect these anisotropic components whose magnitudes are as small as ∼ 1 percent of the detector noise level in terms of the non-dimensional energy density ΩGW (f).