Many-body effects on dense matter with hyperons at finite temperature

TL;DR

This work extends the Many-Body Forces (MBF) model to finite temperature to study dense baryonic matter including hyperons and finite-entropy effects. By employing a scalar MBF (S) parameterization with a density-dependent, field-controlled coupling, the authors explore three meson-hyperon coupling schemes (U, M, SU(6)) and two representative ζ parameter values to map out the EoS, speed of sound, compressibility, and adiabatic index across temperatures. They compute EoSs and solve Tolman-Oppenheimer-Volkoff equations to obtain mass-radius relations for hot and cold neutron stars, showing that ζ=0.040 yields stiffer, observationally consistent NSs even with hyperons, while ζ=0.129 often fails to meet heavy-pulsar constraints when hyperons are included. Finite-temperature effects delay hyperon onset, modify thermal profiles, and preserve causality, illustrating the MBF model’s utility for proto-neutron-star evolution and dense-matter thermodynamics. The results highlight the interplay between many-body forces, hyperon couplings, and temperature in shaping NS structure and provide a pathway for incorporating additional physics such as thermal mesons and magnetic fields in future work.

Abstract

In this work, we present the first extension of the Many-Body Forces (MBF) Model to finite temperature. The MBF Model describes nuclear matter in a relativistic quantum hadrodynamics formalism that takes many-body forces into account through a field dependence of the nuclear interaction coupling constants. Assuming nuclear matter to be charge neutral, beta-equilibrated, and populated by the baryon octet, electrons, and muons, we explore the parameters of the model, three different hyperon coupling schemes (also introduced here for the first time in MBF), and temperature effects to describe basic properties of nuclear matter, including the speed of sound, compressibility, and adiabatic index. We also investigate the mass-radius relation of compact stars by solving the Tolman-Oppenheimer-Volkoff equations at zero and finite temperature, including scenarios with fixed entropy per baryon. Our original results at finite temperature open the path to a new description of proto-neutron stars.

Figures (20)

• Figure 1: Schematic representation of the low/high-baryon-density and low/medium-temperature sector of the QCD phase diagram, where strongly interacting matter is dominated by baryonic degrees of freedom. Light quarks ($u$ and $d$) are shown in white, such that ordinary nucleons are depicted as bound triplets of three white circles. The onset of strangeness is illustrated through the appearance of strange quarks ($s$), represented in gray; hyperons are therefore indicated as composite states containing one or two gray circles in combination with the light-quark constituents. The background red gradient points toward increasing energy scale.
• Figure 2: SET 1 (Equations of state): Pressure ($p$) as a function of energy density ($\varepsilon$) for different proto-neutron star evolution snapshots, particle composition, and hyperon couplings. The different panels show different MBF (left vs. right) and strange scalar meson parameterizations (top vs. bottom).
• Figure 3: SET 2 (Equations of state): Same as Fig. \ref{['EOSgeral']} but now the different panels show different evolution snapshots (left/center/right) and strange scalar meson parameterizations (top vs. bottom).
• Figure 4: SET 1 (Fraction of strangeness): Fraction of strangeness ($Y_S$) as a function of baryon density ($n_B$) for different proto-neutron star evolution snapshots, particle composition, and hyperon couplings. The different panels show different MBF (left vs. right) and strange scalar meson parameterizations (top vs. bottom).
• Figure 5: SET 2 (Fraction of strangeness): Same as Fig. \ref{['FSgeral']} but now the different panels show different evolution snapshots (left/center/right) and strange scalar meson parameterizations (top vs. bottom).