Conserved cosmological relic abundance
= Conserved cosmological relic abundance
{title2=$Y=n/s$}
If relic particle number and reference-gas <entropy> are separately conserved in a <comoving volume>, their ratio $Y=n/s$ is constant. A decay or <entropy> injection can change it. The reference entropy is that of the specified thermal sector, not necessarily the entropy of the decoupled relic itself.