Deconfinement Transition Effects on Cosmological Parameters and Primordial Gravitational Wave Spectrum

TL;DR

This paper investigates how the QCD deconfinement transition in the early universe influences cosmological parameters and the primordial gravitational wave spectrum, using lattice QCD data and detailed modeling.

Contribution

It provides a detailed analysis of the impact of the QCD crossover transition on cosmological scalars and gravitational waves, refining previous models with lattice QCD and hadron resonance gas data.

Findings

Deconfinement affects the behavior of cosmological parameters near the transition.

The primordial gravitational wave spectrum is significantly modified by the QCD transition.

Lattice QCD data improves the accuracy of the transition's impact on cosmology.

Abstract

The cosmological evolution can be described in terms of directly measurable cosmological scalar parameters (deceleration $q$, jerk $j$, snap $s$, etc...) constructed out of high order derivatives of the scale factor. Their behavior at the critical temperature of the Quantum Chromodynamics (QCD) phase transition in early universe could be a specific tool to study the transition, analogously to the fluctuations of conserved charges in QCD. We analyze the effect of the crossover transition from quarks and gluons to hadrons in early universe on the cosmological scalars and on the gravitational wave spectrum, by using the recent lattice QCD equation of state and including the electroweak degrees of freedom and different models of dark matter. Near the transition the cosmological parameters follow the behavior of QCD trace anomaly and of the speed of sound of the entire system. The effects of deconfinement turn out to be more relevant for the modification of the primordial spectrum of gravitational waves and our complete analysis, based on lattice QCD simulations and on the hadron resonance gas below the critical temperature, refines previous results.