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arXiv · 2506.16684

Chiral Invariant Mass Constraints from HESS J1731 347 in an Extended Parity Doublet Model with Isovector Scalar Meson

Yuk-Kei Kong·Bikai Gao·Masayasu Harada
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Abstract

The recent discovery of a central compact object (CCO) within the supernova remnant HESS J1731-347, with mass $0.77^{+0.20}_{-0.17} \ M_\odot $ and radius $10.4^{+0.86}_{-0.78}$ km is the lightest and smallest compact object ever observed. We identify it as an ultra-light Neutron star (NS) and constrain the chiral invariant mass of nucleon $m_0$ from the observational data of NS using an extended parity doublet model with including the isovector scalar meson $a_0(980)$. We study the higher order asymmertic matter properties such as the symmetry incompressibility $K_{sym}$ and the symmetry skewness $Q_{sym}$ in the presence of $a_0$ meson. We find that $K_{sym}$ and $Q_{sym}$ is sensitive to the chiral invariant mass of nucleon $m_0$ in the presence of $a_0$ meson. We show that the equation of state in the present model satisfies all observational constraints within $2σ$ credible region including the HESS J1731-347 observation, as well as the constraint from $K_{sym}$ when $740 \,\text{ MeV} \lesssim m_0 \lesssim 860 \,\text{ MeV}$ for $L_0 = $ 57.7 MeV. Yet, the $1σ$ constraint from neutron stars appears to be not fully compatible with the constraint from $K_{sym}$ from the present model.

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Yuk-Kei Kong, Bikai Gao, Masayasu Harada. 2025-06-20. Chiral Invariant Mass Constraints from HESS J1731 347 in an Extended Parity Doublet Model with Isovector Scalar Meson. https://arxiv.org/abs/2506.16684

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