A hadron-quark hybrid model reliable for the EoS in $\mu_{B} \leq 400$ MeV

TL;DR

This paper introduces a simple hadron-quark hybrid model that accurately reproduces lattice QCD results for the equation of state at baryon chemical potentials up to 400 MeV and predicts the transition behavior at higher densities.

Contribution

The paper presents a novel, simplified hybrid model combining an independent-quark model and an improved excluded-volume hadron resonance gas model, with a chemical potential independent switching function.

Findings

Successfully reproduces lattice QCD results for EoS at μ_B ≤ 400 MeV.

Predicts the chiral crossover region for 400 ≤ μ_B ≤ 800 MeV.

Provides transition lines from isentropic trajectories up to μ_B = 800 MeV.

Abstract

We present a simple version of hadron-quark hybrid (HQH) model in the $\mu_B$--$T$ plain, where $T$ is temperature and $\mu_{B}$ is the baryon-number chemical potential. The model is composed of the independent-quark model for quark-gluon states and an improved version of excluded-volume hadron resonance gas (EV-HRG) model for hadronic states. In the improved version of EV-HRG, the pressure has charge conjugation and is obtained by a simple analytic form. The switching function from hadron states to quark-gluon states in the present model has no chemical potential dependence. The simple HQH model is successful in reproducing LQCD results on the transition region of chiral crossover and the EoS in $\mu_{B} \leq 400$ MeV. We then predict the chiral-crossover region in $400 \leq \mu_{B} \leq 800$ MeV. We also predict a transition line derived from isentropic trajectories in $0 \leq \mu_{B} \leq 800$ MeV and find that the effect of strangeness neutrality is small there.