Bulk viscosity of baryonic matter with trapped neutrinos

Journal Article · 22 November 2019 · Physical Review. D.

DOI: https://doi.org/10.1103/physrevd.100.103021 · OSTI ID:1800307

Alford, Mark  ^[1]; Harutyunyan, Arus  ^[2]; Sedrakian, Armen  ^[3]

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1. Washington Univ., St. Louis, MO (United States); OSTI
2. Armenia and Yerevan State University (Armenia)
3. Frankfurt Institute for Advanced Studies (Germany); University of Wroclaw (Poland)

Here, we study bulk viscosity arising from weak current Urca processes in dense baryonic matter at and beyond nuclear saturation density. We consider the temperature regime where neutrinos are trapped and therefore have nonzero chemical potential. We model the nuclear matter in a relativistic density functional approach, taking into account the trapped neutrino component. We find that the resonant maximum of the bulk viscosity would occur at or below the neutrino trapping temperature, so in the neutrino trapped regime the bulk viscosity decreases with temperature as $$T^{–2}$$, this decrease being interrupted by a drop to zero at a special temperature where the proton fraction becomes density-independent and the material scale-invariant. The bulk viscosity is larger for matter with lower lepton fraction, i.e., larger isospin asymmetry. We find that bulk viscosity in the neutrino-trapped regime is smaller by several orders of magnitude than in the neutrino-transparent regime, which implies that bulk viscosity in neutrino-trapped matter is probably not strong enough to affect significantly the evolution of neutron star mergers. This also implies weak damping of gravitational waves emitted by the oscillations of the post-merger remnant in the high-temperature, neutrino-trapped phase of evolution.

• Research Organization: Washington Univ., St. Louis, MO (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP); Deutsche Forschungsgemeinschaft (DFG)
• Grant/Contract Number: FG02-05ER41375
• OSTI ID: 1800307
• Journal Information: Physical Review. D., Journal Name: Physical Review. D. Journal Issue: 10 Vol. 100; ISSN 2470-0010
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English