Planck Constraints on Axion-Like Particles through Isotropic Cosmic Birefringence

Understand

We present constraints on isotropic cosmic birefringence induced by axion-like particles (ALPs), derived from the analysis of cosmic microwave background (CMB) polarization measurements obtained with the high-frequency channels of Planck.

• Recent measurements report a hint of isotropic cosmic birefringence, though its origin remains uncertain.
• The detailed dynamics of ALPs can leave characteristic imprints on the shape of the $EB$ angular power spectrum, which can be exploited to constrain specific models of cosmic birefringence.
• We first construct a multi-frequency likelihood that incorporates an intrinsic nonzero $EB$ power spectrum.