Parity-odd CMB Correlations induced by a Chiral Gravitational Wave Background

We investigate weak lensing effects of a chiral gravitational wave background (GWB) as a new mechanism for generating parity-odd correlations in the cosmic microwave background (CMB). Accounting for both photon deflection and polarization rotation, we derive the resulting parity-odd EB and TB angular power spectra. For representative GWB energy density spectra, we find parameter choices that provide good fits to existing measurements. This mechanism provides a potential observational probe of chiral GWB, which can arise in a wide range of theoretical scenarios.