Atsuhisa Ota (Cambridge)
In this talk, I will present a new method to test the statistical isotropy in the early Universe with the cosmic microwave background spectral y-distortion, which is known as the Compton-y parameter of the CMB energy spectrum. Based on second-order cosmological perturbation theory, I will show that the 1-point ensemble averages of the y-distortion anisotropies vanish for the statistically "isotropic" perturbations. Then, I will present that they do not vanish for the statistically "anisotropic" perturbations and that they are directly related to the anisotropic part of the primordial density powerspectrum. In particular, I will show that the quadrupole anisotropy in the primordial density powerspectrum leaves the quadrupole anisotropy in the CMB y distortions.