Impact of symmetry energy on sound speed and spinodal decomposition in dense neutron-rich matter

Journal Article · 25 April 2023 · European Physical Journal. A, Hadrons and Nuclei (Online)

DOI: https://doi.org/10.1140/epja/s10050-023-01010-x · OSTI ID:1997069

Zhang, Nai-Bo ^[1]; Li, Bao-An ^[2]

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1. Southeast University, Nanjing (China)
2. Texas A & M University, Commerce, TX (United States)

Using a meta model for nuclear Equation of State (EOS) with its parameters constrained by astrophysical observations and terrestrial nuclear experiments, we examine effects of nuclear EOS especially its symmetry energy $$E$$_sym($$ρ$$) term on the speed of sound squared $$C$$ $$^2_s$$($$ρ$) and the critical density ρt where $$C$$ $$^2_s$$($$ρ_t$$) vanishes (indicating the onset of spinodal decomposition) in both dense neutron-rich nucleonic matter relevant for relativistic heavy-ion collisions and the cold $$n$$ + $$p$$ + $$e$$ + $$μ$$ matter in neutron stars at $$β$$- equilibrium. Unlike in nucleonic matter with fixed values of the isospin asymmetry $$δ$$, in neutron stars with a density dependent isospin profile $$δ$$($$ρ$$) determined consistently by the $$β$$-equilibrium and charge neutrality conditions, the $$C$$ $$^2_s$$($$ρ$) almost always show a peak and then vanishes at $$ρ_t$$. Furthermore, the latter strongly depends on the high-density behavior of $$E$$_sym($$ρ$$) if the skewness parameter $$J$$₀ characterizing the stiffness of high-density symmetric nuclear matter (SNM) EOS is not too far above its currently known most probable value of about -190 MeV inferred from recent Bayesian analyses of neutron star observables. Moreover, in the case of having a super-soft $$E$$_sym($$ρ$$) that is decreasing with increasing density above about twice the saturation density of nuclear matter, the $$ρ$$_$$t$$ is significantly lower than the density where the $$E$$_sym($$ρ$$) vanishes (indicating the onset of isospin-separation instability and pure neutron matter formation) in neutron star cores.

• Research Organization: Texas A & M University, Commerce, TX (United States); Texas A&M University-Commerce, TX (United States)
• Sponsoring Organization: USDOE Office of Science (SC); National Natural Science Foundation of China (NSFC); Shandong Provincial Natural Science Foundation
• Grant/Contract Number: SC0013702; SC0009971; 12005118; ZR2020QA085
• OSTI ID: 1997069
• Alternate ID(s): OSTI ID: 2280882
• Journal Information: European Physical Journal. A, Hadrons and Nuclei (Online), Vol. 59, Issue 4; ISSN 1434-601X
• Publisher: Springer NatureCopyright Statement
• Country of Publication: United States
• Language: English