Chiral symmetry restoration and hyperon suppression in neutron stars

TL;DR

This paper explores how chiral symmetry restoration influences hyperon emergence in neutron stars, proposing that chiral dynamics can resolve the hyperon puzzle by delaying hyperon onset and avoiding equation of state softening.

Contribution

The study introduces a systematic approach using the $SU(3)$ parity doublet model to connect chiral symmetry restoration with hyperon suppression in neutron star matter, offering a natural solution to the hyperon puzzle.

Findings

Hyperon onset density is highly sensitive to the chiral invariant mass $m_0$.

For $m_0=500$ MeV, hyperons appear at 1.9$n_0$; for $m_0 extgreater 750$ MeV, hyperons appear above 5$n_0$.

Delayed hyperon emergence leads to matter deconfinement before hyperon population, avoiding EoS softening.

Abstract

The ``hyperon puzzle'' remains a fundamental challenge in nuclear astrophysics. We investigate hyperon emergence in neutron star matter using the $SU(3)$ parity doublet model with chiral representation $(3,\bar{3}) + (\bar{3},3)$. This framework naturally incorporates chiral symmetry restoration and provides a systematic description of baryon masses in dense matter through the interplay between the chiral condensate and the chiral invariant mass $m_0$. We find that the hyperon onset density exhibits strong sensitivity to $m_0$: for $m_0 = 500$ MeV, hyperons first appear at $1.9n_0$ while for $m_0 \gtrsim 750$ MeV, hyperons emerge only above $5n_0$. This delayed onset arises from the weakened density dependence of baryon masses at larger $m_0$ values. When the hyperon onset density exceeds the expected quark-hadron transition range ($2$--$5n_0$), matter undergoes deconfinement before hyperons populate, avoiding the EoS softening while maintaining consistency with massive neutron star observations. Our results demonstrate that chiral dynamics provides a natural resolution to the hyperon puzzle without requiring ad hoc repulsive hyperon interactions.