New solution to the hyperon puzzle of neutron stars: Quantum many-body effects

TL;DR

The paper tackles the hyperon puzzle by applying a Dyson–Schwinger equation framework to dense baryonic matter, capturing quantum many-body effects from strong baryon–meson interactions. This approach yields a stiff, hyperon-containing neutron-star EOS with $M_{\mathrm{max}} \approx 2.59\,M_{\odot}$, while maintaining hyperon presence and low proton/hyperon fractions that suppress direct Urca cooling. The results reconcile high-mass neutron stars with hyperons and predict slow cooling unless direct Urca processes are triggered, aligning with observational constraints like NICER radii. The study highlights the importance of nonperturbative many-body dynamics and sets the stage for future refinements including rotation, magnetic fields, and energy–momentum dependent vertices.

Abstract

The hyperon puzzle refers to the challenge of reconciling the existence of hyperons in neutron star cores and the observed high masses of neutron stars. The recent discovery of PSR J0952-0607 ($2.35\pm0.17 M_{\odot}$) has intensified this challenge. Existing solutions fail to achieve such a high mass, and often predict unrealistically fast cooling that is at odds with observations. Here, we propose a novel solution to the hyperon puzzle. Using the Dyson-Schwinger equation approach, we incorporate the quantum many-body effects caused by strong baryon-meson interactions into the equation of state for cold baryonic matter and find it stiff enough to support a maximum hyperon-star mass of $M_{\mathrm{max}} \approx 2.59 M_{\odot}$, which can explain all the observed high neutron-star masses. The resulting proton and hyperon fractions are remarkably low, thus the nucleonic and hyperonic direct Urca processes are significantly suppressed. As a result, fast cooling typically does not occur in ordinary neutron stars.

Figures (5)

• Figure 1: Feynman diagrams for one-loop self-energy corrections to the $\sigma$ meson mass. Solid line represents free baryon propagator. Dashed (dotted) line represents free $\sigma$ ($\omega$) meson propagator. Corrections of (a), (b), (c), and (d) come from baryon-$\sigma$ coupling, self-coupling $g_{3}\sigma^{3}$, self-coupling $g_{4}\sigma^{4}$, and cross-coupling $g_{22}\sigma^{2}\omega^{2}$, respectively.
• Figure 2: Particle fractions versus baryon density $n^{\ast}_{\mathrm{F}}$ in unit of $n_{\mathrm{B}0}$. The hL60 (L60) model refers to $\sigma\omega\rho2L60$ model with (without) hyperons. The hL80 (L80) model refers to $\sigma\omega\rho2L80$ model with (without) hyperons. Shadowed regions marked with nDU (hDU) illustrate the uncertain lower limit of the threshold fractions for nucleonic (hyperonic) DU processes.
• Figure 3: Comparison between HS EOSs and NS EOSs in terms of the pressure $P$ versus the energy-density $\epsilon$.
• Figure 4: Comparison between the theoretical results of M-R relations obtained from six models (hL60, hL80, hL87.56, L60, L80, and L87.56) and some recent astrophysical observations of compact stars.
• Figure 5: Ratios of effective baryon masses to bare masses versus normalized baryon density $n^{\ast}_{\mathrm{F}}/n_{\mathrm{B}0}$ for $\sigma\omega\rho L80$ model.