Impacts of the U(1)A anomaly on nuclear and neutron star equation of state based on a parity doublet model

Bikai Gao, Takuya Minamikawa, Toru Kojo, Masayasu Harada

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We examine the role of the U(1)A anomaly in a parity doublet model of nucleons which include the chiral variant and invariant masses. Our model expresses the U(1)A anomaly by the Kobayashi-Maskawa-'t Hooft (KMT) interaction in the mesonic sector. After examining the roles of the KMT term in vacuum, we discuss its impacts on nuclear equations of state (EOS). The U(1)A anomaly increases the masses of the η′ and σ mesons and enhances the chiral symmetry breaking. Also, the U(1)A anomaly enlarges the energy difference between chiral symmetric and symmetry broken vacuum; in turn, the chiral restoration at high density adds a larger energy density (often referred as a bag constant) to EOSs than in the case without the anomaly, leading to softer EOSs. Including these U(1)A effects, we update the previously constructed unified equations of state that interpolate the nucleonic EOS at nB≤2n0 (n0=0.16fm-3; nuclear saturation density) and quark EOS at nB≥5n0. The unified EOS is confronted with the observational constraints on the masses and radii of neutron stars. The softening of EOSs associated with the U(1) anomaly reduces the overall radii, relaxing the previous constraint on the chiral invariant mass m0. Including the attractive nonlinear ρ-ω coupling for the reduced slope parameter in the symmetry energy, our new estimate is 400MeV≤m0≤700MeV, with m0 smaller than our previous estimate by ≈200 MeV.

Original languageEnglish
Article number065205
JournalPhysical Review C
Issue number6
Publication statusPublished - 2022 Dec

ASJC Scopus subject areas

  • Nuclear and High Energy Physics


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