Bulk viscosity of two-color superconducting quark matter in neutron star mergers

TL;DR

This paper investigates the bulk viscosity of color superconducting quark matter in neutron star mergers, revealing a resonant peak at around 5 MeV that can significantly influence postmerger dynamics.

Contribution

It models quark matter using an improved Nambu--Jona-Lasinio framework and calculates bulk viscosity considering weak-interaction processes, highlighting effects on neutron star merger evolution.

Findings

Bulk viscosity peaks at T~5 MeV affecting damping times.

Resonant damping times can be below 10 ms.

Results are similar to nuclear matter damping predictions.

Abstract

We study the bulk viscosity of moderately hot and dense, neutrino-transparent color superconducting quark matter arising from weak-interaction-driven direct URCA processes. The quark matter is modeled using the Nambu--Jona-Lasinio model improved to account for vector and 't Hooft interactions as well as antisymmetric pairing among the red/green up and down quarks. The unpaired excitations are the strange quarks and the blue up or down quarks. We compute the relaxation rates associated with $d$ and $s$-quark decay and electron capture processes on $u$ quark for blue color. The resulting bulk viscosity for density oscillations in the 1--10\,kHz range shows a resonant peak at $T\sim 5\,\MeV$, and the damping time may drop below 10 ms. This is short enough to affect the postmerger evolution and is very similar to the damping predicted in nuclear matter.