Testing parity-violating mechanisms with cosmic microwave background experiments

Chiral gravity and cosmological birefringence both provide physical mechanisms to produce parity-violating $TB$ and $EB$ correlations in the cosmic microwave background (CMB) temperature/polarization. Here, we study how well these two mechanisms can be distinguished if nonzero $TB/EB$ correlations are found. To do so, we evaluate the correlation matrix, including new TB-EB covariances. We find that the effects of these two mechanisms on the CMB are highly orthogonal, and can thus be distinguished fairly well in the case of a high-signal-to-noise detection of $TB/EB$ correlations. Appendix B evaluates the relative sensitivities of the $BB$, $TB$, and $EB$ signals for detecting a chiral gravitational-wave background.