POLARBEAR constraints on cosmic birefringence and primordial magnetic fields

The POLARBEAR experiment has set new upper limits on parity violating processes or the existence of an equivalent primordial magnetic field. These would induce anisotropic cosmic birefringence, which convert parity-even (E-modes) to parity-odd (B-modes) of the polarized component of the cosmic microwave background anisotropy. The new limits are important for further constraining models of the early Universe.