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

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 the $u$ quark for blue color. The resulting bulk viscosity for density oscillations in the 1--10 kHz range shows a resonant peak at $T\ensuremath{\sim}5\text{ }\text{ }\mathrm{MeV}$, 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.