Reactions Governing Strangeness Abundance in Primordial Universe

TL;DR

This paper investigates the reaction rates of strangeness production in the early universe and identifies the temperatures at which strangeness remained in chemical equilibrium during the hadronic epoch.

Contribution

It provides a detailed analysis of reaction rates compared to the universe's expansion rate, pinpointing when strangeness production maintained equilibrium in the primordial universe.

Findings

Reaction rates for key processes slow down below the Hubble rate at specific temperatures.

Strangeness was in chemical equilibrium near T ≈ 40 MeV.

Identifies critical temperatures for strangeness freeze-out in the early universe.

Abstract

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.