BICEP / Keck XII: Constraints on axion-like polarization oscillations in the cosmic microwave background

Understand

We present a search for axion-like polarization oscillations in the cosmic microwave background (CMB) with observations from the Keck Array.

• A local axion field induces an all-sky, temporally sinusoidal rotation of CMB polarization.
• A CMB polarimeter can thus function as a direct-detection experiment for axion-like dark matter.
• We develop techniques to extract an oscillation signal.