= CDM density equation in a matter-radiation universe
{c}
{title2=$\delta_C''+\mathcal H\delta_C'=4\pi Ga^2(\rho_C\delta_C+2\rho_R\delta_R)$}
In <Synchronous gauge in cosmology> with coordinates comoving with <cold dark matter>, the linearized <Einstein field equations> and matter conservation give the displayed density equation. Primes denote <conformal time> derivatives. The radiation term contains its pressure contribution and cannot be dropped on <superhorizon scales> merely because radiation oscillates after <cosmological horizon entry>.
Back to article page
