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Title: Cosmic Birefringence and Axion
Speaker: Prof. Fuminobu Takahashi (Tohoku U.)
Abstract: Recently, it was reported that the Planck 2018 polarization data of cosmic microwave background (CMB) favors a nonzero value of isotropic cosmic birefringence (CB) with statistical significance of 2.4 sigma. The observed rotation angle of the CMB polarization can be explained by an axion-like particle that has changed by about the decay constant from the time of recombination to the present. I will introduce two scenarios which naturally explain the hinted isotropic CB. One is the axion domain wall, and the other is an axion coupled to dark matter density. The former also predicts a peculiar anisotropic CB, which can be searched for with future CMB observations.
