I am read the pag 190 of Dodelson bock, where use the following relation(adsbygoogle = window.adsbygoogle || []).push({});

[tex] \rho_{DM}= \rho \frac{y}{y+1} [/tex]. where [tex] y= a/a_{eq}=\rho_{DM}/\rho_{rad}[/tex]

i tried using the tipically relation [tex] \rho = \rho_{rad} a^-4+ \rho_{DM} [/tex]

but, i dont understand,

healp please

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# Dodelson text

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