The Quark-Hadron Transition in the Early Universe

TL;DR

This paper utilizes recent lattice QCD data to determine the Universe's expansion law during the quark-hadron transition, introducing techniques to analyze pressure and energy density and comparing crossover and first-order transition scenarios.

Contribution

It develops a novel method to extract the cosmological expansion law from lattice QCD outputs and relates different temperature regimes for a comprehensive analysis.

Findings

The expansion law during the quark-hadron transition is characterized using lattice data.

Differences between crossover and first-order transition scenarios are minimal but potentially observable with future precision cosmology.

The introduced techniques effectively relate lattice data across temperature ranges for cosmological modeling.

Abstract

We use recent lattice QCD outputs to work out the expansion law of the Universe during the cosmological quark--hadron transition. To do so, a suitable technique to exploit both pressure and energy density data, with the related error bars, is introduced. We also implement suitable techniques to relate the T range where lattice outputs are available with lower and higher T's, for which we test suitable expressions. We finally compare the cosmological behavior found using lattice data with the one obtainable in the case the transition were first order, although not so far from the crossover transition we studied. Differences are small to be tested with cosmological data, but the coming of the era of precision cosmology might open a channel to inspect the QCD transition through them.