Cosmic birefringence test of the Hubble tension

Abstract

A cosmic pseudo-Nambu-Goldstone boson has been proposed to resolve the four-sigma discrepancy between precision measurements of the expansion rate of the universe. We show this solution may also produce a cosmic birefringence (CB) signal in the polarization of the cosmic microwave background (CMB); observations of the CB power spectrum and cross-correlation with the CMB can independently confirm the presence of this new boson. We find significant new contributions to the CB signal, and show that future CMB experiments will greatly improve sensitivity to CB and Hubble tension scenarios.