Bulk viscosity in strong and electroweak matter

TL;DR

This paper calculates the bulk viscosity of matter across a wide temperature and density range using various theories and models, highlighting the significance of electroweak and QCD effects in different regimes.

Contribution

It provides a comprehensive calculation of bulk viscosity incorporating both perturbative and non-perturbative QCD, as well as electroweak contributions, across a broad temperature and density spectrum.

Findings

The dimensionless quantity 9ω₀ζ/Ts decreases exponentially with temperature.

Bulk viscosity non-monotonically increases with density when only QCD effects are considered.

Including all Standard Model contributions, ζ increases nearly linearly with density.

Abstract

For temperatures $T$ ranging from a few MeV up to TeV and energy density $\rho$ up to $10^{16}~$GeV/fm$^3$, the bulk viscosity $\zeta$ is calculated in non-perturbation (up, down, strange, charm, and bottom) and perturbation theories with up, down, strange, charm, bottom, and top quark flavors, at vanishing baryon-chemical potential. To these calculations, results deduced from the effective QCD-like model, the Polyakov linear-sigma model (PLSM), are also integrated in. The PLSM merely comes up with essential contributions for the vacuum and thermal condensations of the gluons and the quarks (up, down, strange, and charm flavors). Furthermore, the thermal contributions of the photons, neutrinos, charged leptons, electroweak particles, and scalar Higgs boson, are found very significant along the entire range of $T$ and $\rho$ and therefore could be well integrated in. We present the dimensionless quantity $9 \omega_0 \zeta/Ts$, where $\omega_0$ is a perturbative scale and $s$ is the entropy density and conclude that $9 \omega_0 \zeta/Ts$ exponentially decreases with increasing $T$. We also conclude that the resulting $\zeta$ with the non-perturbative and perturbative QCD contributions non-monotonically increases with increasing $\rho$. But with nearly-entire standard model contributions considered in the present study, $\zeta$ almost-linearly increases with increasing $\rho$. Apparently, these results offer a great deal to explore in astrophysics, cosmology, and nuclear collisions.