arXiv subjects

Shu-Yu Zuo

Publications and source records attributed to Shu-Yu Zuo.

5 recordsLinked to original sources

arXiv2024

Study of hybrid stars with nonstrange quark matter cores

In this work, under the hypothesis that quark matter may not be strange (Holdom et al. 2018), we adopt a modification of the coupling constant of the four-quark scalar interaction $G\rightarrow G_1+G_2\langle\bar{\psi}\psi\rangle$ in the 2-flavor Nambu-Jona-Lasinio (NJL) model to study nonstrange hybrid stars, where $G_1$ and $G_2$ are two parameters constrained by using the lattice QCD simulation results at the critical temperature and zero chemical potential. The Maxwell construction is used to describe the first-order confinement-deconfinement phase transition in hybrid stars. With recent measurements on neutron star mass, radius, and tidal deformability, the hybrid equation of states are constrained. It is found that pure nonstrange quark matter cores can exist in hybrid stars, possessing $0.026-0.04$ solar mass. The maximum hybrid star mass in the framework of the modified NJL model is about 0.1 solar mass lighter than that in the conventional 2-flavor NJL model. It is argued that the binary neutron stars in GW170817 should be hadron stars.

nucl-th↗

arXiv2023

Nonextensive effects on QCD chiral phase diagram and baryon-number fluctuations within Polyakov-Nambu-Jona-Lasinio model

In this paper, a version of the Polyakov-Nambu-Jona-Lasinio (PNJL) model based on nonextensive statistical mechanics is presented. This new statistics summarizes all possible factors that violate the assumptions of the Boltzmann-Gibbs (BG) statistics to a dimensionless nonextensivity parameter $q$, and when $q$ tends to 1, it returns to the BG case. Within the nonextensive PNJL model, we found that as $q$ increases, the location of the critical end point (CEP) exhibits non-monotonic behavior. That is, for $q<1.15$, CEP moves in the direction of lower temperature and larger quark chemical potential. But for $q>1.15$, CEP turns to move in the direction of lower temperature and lower quark chemical potential. In addition, we studied the moments of the net-baryon number distribution, that is, the variance ($σ^{2}$), skewness (S), and kurtosis ($κ$). Our results are generally consistent with the latest experimental data, especially for $\sqrt{S_{NN}}>19.6\ \mathrm{GeV}$, when $q$ is set to $1.07$.

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arXiv2022

The study of nonstrange quark stars within a modified NJL model

In this work, a modified Nambu-Jona-Lasinio (NJL) model with proper-time regularization is employed to study the structure of nonstrange quark stars. The coupling constant of four-fermion interaction in the conventional NJL model is modified as $G=G_1+G_2\langle\barψψ\rangle$ to highlight the feedback of quark propagator to gluon propagator. To study the dependence of the equation of state (EOS) on this modification as well as the vacuum pressure, we choose nine representative EOSs for comparison. It is found that a smaller $G_1$ leads to a stiffer EOS, and a higher vacuum pressure (i.e., a smaller bag constant) yields a softer EOS at low energy density. It is further shown that the heaviest quark star under this modified NJL model satisfies not only the recent mass measurement of PSR J0740+6620, but also the radius constraints from X-ray timing observations. The corresponding tidal deformability is also in agreement with the observations of GW170817.

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arXiv2020

QCD phase diagram and critical exponents within the nonextensive Polyakov-Nambu-Jona-Lasinio model

We present a nonextensive version of the Polyakov-Nambu-Jona-Lasinio model which is based on the nonextentive statistical mechanics. This new statistics is characterized by a dimensionless nonextensivity parameter $q$ that accounts for all possible effects violating the assumptions of the Boltzmann-Gibbs (BG) statistics (when $q\rightarrow1$, it returns to the BG case). Based on the nonextensive Polyakov-Nambu-Jona-Lasinio model, we discussed the influence of the nonextensive effects on the QCD phase transition, especially on the location of the critical end point (CEP). A new and interesting phenomenon we found is that with the increase of $q$, the CEP position initially shifted toward the direction of larger chemical potential and lower temperature. But then, when $q$ is greater than a critical value $q_{c}$, the CEP position moves in the opposite direction. In other words, as $q$ increases, the CEP position moves in the direction of smaller chemical potential and higher temperature. In addition, we calculated the influence of the nonextensive effects on the critical exponents and found that they remain almost constant with $q$.

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arXiv2020

Strange quark stars within proper time regularized (2+1)-flavor NJL model

In this work we use the equation of state (EOS) of (2+1)-flavor Nambu-Jona-Lasinio (NJL) model to study the structure of the strange quark star. With a new free parameter $α$, the Lagrangian is constructed by two parts, the original NJL Lagrangian and the Fierz transformation of it, as $\mathcal{L}=(1-α)\mathcal{L}_{NJL}+α\mathcal{L}_{Fierz}$. To determine the range of $α$, we compare the binding energies in the 2-flavor and (2+1)-flavor cases. We also consider the constraints of chemical equilibrium and electric charge neutrality in the strange quark star and choose six representative EOSs with different $α$ and $B$ (bag constant) to study their influence on the structure of the strange quark star. As a result, we find that a larger $α$ and a smaller $B$ corresponds to a heavier star with a stiffer EOS. Furthermore, the heaviest strange quark star is in agreement with not only the recent mass observation of PSR J0740+6620 and the X-ray observations on radius measurements, but also the constraint on tidal deformability of GW170817.

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