Isotropic cosmic birefringence from an oscillating axion-like field

Understand

We propose a new mechanism for isotropic cosmic birefringence with an axion-like field that rapidly oscillates during the recombination epoch.

• In conventional models, the field oscillation during the recombination epoch leads to a cancellation of the birefringence effect and significantly suppresses the EB spectrum of the cosmic microwave background (CMB) polarization.
• By introducing an asymmetric potential to the axion, this cancellation becomes incomplete, and a substantial EB spectrum can be produced.
• This mechanism also results in a washout of the EE spectrum, which can be probed in future CMB observations.