Abstract
We investigate the strange particle composition of the expanding early Universe in the hadron epoch Th≈150≥T≥10 MeV. We study strangeness yield in thermal and chemical equilibrium constrained by prescribed conserved entropy per baryon in a charge neutral and strangeness neutral 〈s−s¯〉 Universe. Turning to kinetic processes in a Hubble expanding Universe, we determine the conditions at which at decreasing temperature T individual strangeness producing reactions fall out of detailed balance between decay and back-reaction strangeness production rates: This is done by comparing the relevant reaction rates to the Hubble expansion rate. We allow for weak, electromagnetic, and strong interaction processes. The weak interaction μ±+νμ→K± freezeout is at TfK±=33.8 MeV; the electromagnetic process l−+l+→ϕ freezeout is at Tfϕ=23∼25 MeV; and the hadronic reaction π+π→K freezeout is at TfK=19.8 MeV.
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