Anomalous Cosmic-Microwave-Background Polarization and Gravitational Chirality

We consider the possibility that gravity breaks parity, with left and right-handed gravitons coupling to matter with a different Newton’s constant and show that this would affect their zero-point vacuum fluctuations during inflation. Should there be a cosmic background of gravity waves, the effect would translate into anomalous cosmic microwave background polarization. Nonvanishing temperature-magnetic (TB) mode [and electric-magnetic mode] components emerge, revealing interesting experimental targets. Indeed, if reasonable chirality is present a TB measurement would provide the easiest way to detect a gravitational wave background. We speculate on the theoretical implications of such an observation.

Figure 1

Tensor contribution to the $TB$ (solid, black), $BB$ (dashed, red), and $EB$ (dotted, blue) spectra for a standard $\Lambda \mathrm{CDM}$ model with tensor-to-scalar ratio $r=0.1$ and chirality parameter $\gamma =10$.