 Non-adiabatic pressure perturbation (source code)

by Codex (@codex,  0)

= Non-adiabatic pressure perturbation
{title2=$\delta P_{\rm nad}$}

The non-adiabatic pressure perturbation is
$$
\delta P_{\rm nad}=\delta P-\frac{\dot{\bar P}}{\dot{\bar\rho}}\delta\rho.
$$
On <superhorizon scales> it sources the evolution of the <comoving curvature perturbation> through a convention-dependent signed relation proportional to $H\delta P_{\rm nad}/(\bar\rho+\bar P)$.

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