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

Alford, Mark; Harutyunyan, Arus; Sedrakian, Armen; Tsiopelas, Stefanos

doi:10.3389/fspas.2025.1648066

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

Journal Article · Wed Sep 10 00:00:00 EDT 2025 · Frontiers in Astronomy and Space Sciences

DOI:https://doi.org/10.3389/fspas.2025.1648066· OSTI ID:3015644

^[1]; Harutyunyan, Arus ^[2]; Sedrakian, Armen ^[3]; Tsiopelas, Stefanos ^[4]

Washington University, St. Louis, MO (United States)
Byurakan Astrophysical Observatory (Armenia); Yerevan State University (Armenia)
Frankfurt Institute for Advanced Studies (Germany); University of Wrocław (Poland)
University of Wrocław (Poland)

This work investigates the bulk viscosity of warm, dense, neutrino-transparent, color-superconducting quark matter, where damping of density oscillations in the kHz frequency range arises from weak-interaction-driven direct Urca processes involving quarks. We study the two-flavor red-green paired color-superconducting (2SC) phase, while allowing for the presence of unpaired strange quarks and blue color light quarks of all flavors. Our calculations are based on the SU(3) Nambu–Jona–Lasinio model, extended to include both vector interactions and the ‘t Hooft determinant term. The primary focus is on how variations in the NJL Lagrangian parameters—specifically, the diquark and vector coupling strengths—affect both the static properties of quark matter, such as its equation of state and composition, and its dynamical behavior, including bulk viscosity and associated damping timescales. We find that the bulk viscosity and corresponding damping timescale can change by more than an order of magnitude upon varying the vector coupling by a factor of two at high densities and by a lesser degree at lower densities. This sensitivity primarily arises from the susceptibility of 2SC matter, with a smaller contribution from modifications to the weak interaction rates. In comparison, changes in the diquark coupling have a more limited impact. The damping of density oscillations in 2SC matter is similar quantitatively to nucleonic matter and can be a leading mechanism of dissipation in merging hybrid stars containing color superconducting cores.

View Accepted Manuscript (DOE)

Research Organization:: Washington University, St. Louis, MO (United States)

Sponsoring Organization:: Deutsche Forschungsgemeinschaft (DFG); Higher Education and Science Committee (HESC) of the Republic of Armenia; Polish National Science Centre (NCN); USDOE Office of Science (SC), Nuclear Physics (NP)

Grant/Contract Number:: FG02-05ER41375

OSTI ID:: 3015644

Journal Information:: Frontiers in Astronomy and Space Sciences, Journal Name: Frontiers in Astronomy and Space Sciences Vol. 12; ISSN 2296-987X

Publisher:: Frontiers Media SACopyright Statement

Country of Publication:: United States

Language:: English

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