Charm contribution to bulk viscosity

TL;DR

This paper estimates how charm quarks contribute to the bulk viscosity of quark-gluon plasma in heavy ion collisions, highlighting their potential impact during early hydrodynamic expansion at high temperatures.

Contribution

It provides the first estimate of charm quark effects on bulk viscosity using an effective kinetic theory framework, extending previous light parton analyses.

Findings

Charm quarks can significantly increase bulk viscosity at T > 600 MeV.

The relevant timescale for charm effects is less than 20 fm/c.

Charm contributions become relevant during the early stages of plasma evolution.

Abstract

In the range of temperatures reached in future heavy ion collision experiments, hadronic pair annihilations and creations of charm quarks may take place within the lifetime of the plasma. As a result, charm quarks may increase the bulk viscosity affecting the early stages of hydrodynamic expansion. Assuming thermalization, we estimate the charm contribution to bulk viscosity within the same effective kinetic theory framework in which the light parton contribution has been computed previously. The time scale at which this physics becomes relevant is related to the width of the transport peak associated with the trace anomaly correlator, and is found to be < 20 fm/c for T > 600 MeV.