# Hadron contribution to effective degrees of freedom in early Universe

In transition from quark-gluon plasma to hadron gas in the early Universe, the value of the effective degrees of freedom $g_{\star}$ decreases abruptly. This seems to me like a sort of decoupling: when quarks and gluons are free, they are in thermal equlibrium, but when they get together to form hadrons they "decouple" and stop contributing to the effective degrees of freedom. Why?

So actually $g_{\star}$ is the effective relativistic degrees of freedom, and hadrons like $p$ or $n$ are not relativistic, whereas quarks like $u$ or $d$ are relativistic.