Quark-Gluon Plasma as the Possible Source of Cosmological Dark Radiation

TL;DR

This paper investigates the potential role of the quark-gluon plasma in contributing to cosmological dark radiation by constraining unknown degrees of freedom through lattice-QCD and kinetic theory, linking early universe physics with laboratory QGP studies.

Contribution

It introduces a novel approach to connect the effective number of neutrinos with the QGP phase transition, providing bounds on unknown particle couplings based on lattice-QCD data.

Findings

Constraints on unknown particle couplings near quark-gluon hadronization.

Bounds on dark radiation contributions from QGP phase transition.

Implications for laboratory QGP experiments and cosmology.

Abstract

The effective number of neutrinos, $N_{\text{eff}}$, obtained from CMB fluctuations accounts for all effectively massless degrees of freedom present in the Universe, including but not limited to the three known neutrinos. Using a lattice-QCD derived QGP equation of state, we constrain the observed range of $N_{\text{eff}}$ in terms of the the freeze-out of unknown degrees of freedom near to quark-gluon hadronization. We explore limits on the coupling of these particles, applying methods of kinetic theory. We present bounds on the coupling of such particles and discuss the implications of a connection between $N_{\text{eff}}$ and the QGP transformation for laboratory studies of QGP.