Cosmological Strangeness Abundance

TL;DR

This paper explores the production and freezeout conditions of strange particles in the early Universe during the hadron epoch, analyzing equilibrium states and reaction decoupling temperatures across different interactions.

Contribution

It provides a detailed analysis of strangeness yield and freezeout conditions for various reactions in the early Universe, considering multiple interaction types and their impact on particle abundances.

Findings

Weak interaction freezeout at 33.8 MeV

Electromagnetic process freezeout at 23-25 MeV

Hadronic reaction freezeout at 19.8 MeV

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 $\mu^\pm+\nu_{\mu}\rightarrow K^\pm$ freezeout is at $T_f^{K^\pm}=33.8\,\mathrm{MeV}$; the electromagnetic process $l^-+l^+\rightarrow\phi$ freezeout is at $T_f^\phi=23\sim25\,\mathrm{MeV}$; and the hadronic reaction $\pi+\pi\rightarrow K$ freezeout is at $T_f^K=19.8\,\mathrm{MeV}$.