Photon dipole
= Photon dipole
{title2=$\Theta_1$}
The photon dipole represents the bulk velocity of the radiation. In tight coupling to baryons, $v_b=-3\Theta_1$ under the convention used here.
= Photon dipole
{title2=$\Theta_1$}
The photon dipole represents the bulk velocity of the radiation. In tight coupling to baryons, $v_b=-3\Theta_1$ under the convention used here.