Suprathermal viscosity of dense matter

TL;DR

This paper investigates how non-linear, supra-thermal bulk viscosity in dense matter can stabilize unstable modes in compact stars, revealing significant enhancement especially in hadronic and quark matter phases.

Contribution

It introduces a detailed analysis of non-linear bulk viscosity effects at large amplitudes, extending previous work to hadronic matter and various color superconducting phases.

Findings

Supra-thermal bulk viscosity is strongly enhanced at large amplitudes.

Enhanced viscosity can saturate unstable modes in compact stars.

The effect is more pronounced in hadronic matter than in strange quark matter.

Abstract

Motivated by the existence of unstable modes of compact stars that eventually grow large, we study the bulk viscosity of dense matter, taking into account non-linear effects arising in the large amplitude regime, where the deviation mu_Delta of the chemical potentials from chemical equilibrium fulfills mu_Delta > T. We find that this supra-thermal bulk viscosity can provide a potential mechanism for saturating unstable modes in compact stars since the viscosity is strongly enhanced. Our study confirms previous results on strange quark matter and shows that the suprathermal enhancement is even stronger in the case of hadronic matter. We also comment on the competition of different weak channels and the presence of suprathermal effects in various color superconducting phases of dense quark matter.