Speaker
Description
The properties of dense, neutron-rich matter are strongly influenced by the isovector structure of the nuclear interaction. In particular, the isovector scalar meson a0(980) (also known as the delta meson) modifies the neutron–proton effective mass splitting and significantly affects the behavior of isospin-asymmetric matter. In this talk, we construct an extended parity doublet model including the a0 meson to investigate its role in asymmetric matter and explore its implications for dense baryonic systems. Finite nuclei and neutron stars provide complementary probes of low- and high-density matter, respectively.
We construct a hadron–quark crossover equation of state including the a0 meson and analyze neutron-star properties. We examine how the a0 meson modifies neutron-star structure, the symmetry energy, and higher-order symmetry-energy parameters. Using neutron-star observational data, we constrain the chiral invariant mass of the nucleon, m0. In particular, motivated by the recent observation of an unusually light and compact neutron-star candidate in HESS J1731−347, we show that the 1 sigma data from this source impose a remarkably narrow constraint on the allowed values of m0 and L0 within the crossover framework: 830 MeV < m0 < 900 MeV for L0 = 40 MeV, and 850 MeV < m0 < 890 MeV for L0 = 45 MeV.
We also investigate the role of the a0 meson in finite nuclei. By fitting the model to experimental data, including binding energies and charge radii, we further constrain m0 and examine how the isovector scalar channel influences finite-nucleus observables such as neutron-skin thickness.
Taken together, these results demonstrate how the isovector scalar interaction shapes asymmetric matter across a wide density range and determine how neutron-star and finite-nucleus data constrain the chiral invariant mass in dense baryonic matter.