Strangness production processes can balance natural strangeness decay in the early hadronic Universe. Comparing to the characteristic Hubble time $1/H$, the reaction rates for $\mu^\pm+\nu_{ \mu}\rightarrow K^\pm$, $l^-+l^+\rightarrow\phi$, and $\pi+\pi\rightarrow K$ in sequence become slower than expansion rate at $T=33.9\,\mathrm{ MeV}$, $T=25\,\mathrm{ MeV}$ and $T=20\,\mathrm{ MeV}$ respectively. This means that in the antibaryon annihilation epoch near to $T\simeq 40\,\mathrm{ MeV}$ strangeness is in chemical equilibrium.
Categories: hep-ph