Supersonic baryon-CDM velocities and CMB B-mode polarization

Understand

It has recently been shown that supersonic relative velocities between dark matter and baryonic matter can have a significant effect on formation of the first structures in the universe.

• If this effect is still non-negligible during the epoch of hydrogen reionization, it generates large-scale anisotropy in the free electron density, which gives rise to a CMB B-mode.
• We compute the B-mode power spectrum and find a characteristic shape with acoustic peaks at l ~ 200, 400, ...
• The amplitude of this signal is a free parameter which is related to the dependence of the ionization fraction on the relative baryon-CDM velocity during the epoch of reionization.