Bulk viscosity from Urca processes: n p e μ matter in the neutrino-transparent regime

Journal Article · 12 October 2023 · Physical Review. D.

DOI: https://doi.org/10.1103/physrevd.108.083019 · OSTI ID:2092370

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

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

We study the bulk viscosity of moderately hot and dense, neutrino-transparent relativistic npeμ matter arising from weak-interaction direct Urca processes. This work parallels our recent study of the bulk viscosity of npeμ matter with a trapped neutrino component. The nuclear matter is modeled in a relativistic density functional approach with two different parametrizations—DDME2 (which does not allow for the low-temperature direct-Urca process at any density) and NL3 (which allows for low-temperature direct-Urca process above a low-density threshold). Here, we compute the equilibration rates of Urca processes of neutron decay and lepton capture, as well as the rate of the muon decay, and find that the muon decay process is subdominant to the Urca processes at temperatures T ≥ 3 MeV in the case of DDME2 model and T ≥ 1 MeV in the case of NL3 model. Thus, the Urca-process-driven bulk viscosity is computed with the assumption that pure leptonic reactions are frozen. As a result the electronic and muonic Urca channels contribute to the bulk viscosity independently and at certain densities the bulk viscosity of npeμ matter shows a double-peak structure as a function of temperature instead of the standard one-peak (resonant) form. In the final step, we estimate the damping timescales of density oscillations by the bulk viscosity. We find that, e.g., at a typical oscillation frequency f = 1~kHz, the damping of oscillation is most efficient at temperatures 3 ≤ T ≤ 5~MeV and densities n_B ≤ 2n₀ where they can affect the evolution of the post-merger object.

• Research Organization: Washington University in St. Louis, MO (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP)
• Grant/Contract Number: FG02-05ER41375
• OSTI ID: 2092370
• Alternate ID(s): OSTI ID: 2438411
• Journal Information: Physical Review. D., Journal Name: Physical Review. D. Journal Issue: 8 Vol. 108; ISSN 2470-0010
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English