= Suppressed cold-matter forcing by rapid radiation oscillations
{title2=$\Delta_{c,\rm osc}=O[\Delta_r/(k\tau)^2]$}
In deep <radiation domination>, an oscillatory radiation density source in the matter equation has order $\Delta_r/\tau^2$ and frequency of order $k$. Its rapidly varying particular response is therefore of order $\Delta_r/(k\tau)^2$. For $k\tau\gg1$ it does not control the secular matter growth, though forcing near horizon entry sets the constant and logarithmic homogeneous amplitudes.
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