Cosmological Strangeness Abundance

Abstract

We investigate the strange particle composition of the early Universe in the hadron epoch $T_h\approx 150\ge T\ge 10$\,MeV. We study strangeness yield in thermal and chemical equilibrium constrained by prescribed entropy per baryon in a charge neutral and strangeness neutral $\langle s-\bar s\rangle$ Universe. Turning to kinetic processes in a Hubble expanding Universe, we determine conditions at which individual strangeness producing reactions fall out of detailed balance between decay and back-reaction strangeness production rates in presence of decreasing temperature $T$; we allow for weak, electromagnetic, and strong interaction processes. The weak interaction $μ^\pm+ν_μ\rightarrow K^\pm$ freezeout is at $T_f^{K^\pm}=33.8\,\mathrm{MeV}$; the electromagnetic process $l^-+l^+\rightarrowϕ$ freezeout is at $T_f^ϕ=23\sim25\,\mathrm{MeV}$; and the hadronic reaction $π+π\rightarrow K$ freezeout is at $T_f^K=19.8\,\mathrm{MeV}$.