Cosmic microwave background spectral distortions from Rayleigh scattering at second order

Cosmic microwave background (CMB) spectral distortion from Rayleigh scattering is calculated for the first time in rigorous second-order cosmological perturbation theory. The new spectral distortion is sensitive to acoustic dissipation at 10(-2) < kMpc/h < 1, which slightly extends the scale constrained by the CMB anisotropies. The spectral shape is different from either temperature perturbations or other traditional spectral distortions from Compton scattering, such as y and mu. The new spectral distortion is not formed in the late Universe, unlike the thermal Sunyaev-Zel'dovich effect degenerated with the primordial y distortion since photons must be hot for Rayleigh scattering. Therefore, ideal measurements can distinguish the signal from the other effects and extract new information during recombination. Assuming cosmological parameters consistent with the recent CMB anisotropy measurements, we find the new spectral distortion is 6.5 x 10(-3) Jy/sr, which is one order of magnitude smaller than the currently proposed target sensitivity range of Voyage 2050.

Automated summary

This study calculates the spectral distortion of the cosmic microwave background (CMB) caused by Rayleigh scattering for the first time using rigorous second-order cosmological perturbation theory. The new spectral distortion is sensitive to acoustic dissipation and provides additional information beyond the scale constrained by CMB anisotropies.