Baryon Euler equation with Thomson drag
= Baryon Euler equation with Thomson drag
{title2=$\dot v_b+\mathcal H v_b+k\psi=(\dot\tau/R)(v_b-v_\gamma)$}
For the velocity convention $v_\gamma=-\Theta_1$ and $\dot\tau<0$, momentum-conserving <Thomson scattering> gives $\dot v_b+\mathcal H v_b+k\psi=(\dot\tau/R)(v_b-v_\gamma)$. Here $R$ is the <baryon loading parameter>. Its collision force is opposite to the photon force when both are weighted by their enthalpies.