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

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 $T\sim 5\text{MeV}$, 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.

Comments: v2: 6 pages + 4 figures main text, 2 pages + 2 figures supplemental material. Matches version published in Phys. Rev. D. Letters