In this work, we extend the quasiparticle model to include the chemical potential dependence of the coupling constant $\textit{g}$ and consider the density-dependent bag constant $$B_m$$ in order to satisfy the asymptotic freedom feature. By satisfying the absolutely stable condition at zero temperature, we draw the stability region of the strange quark matter (SQM) and describe the recently discovered pulsars PSR J0952-0607, PSR J2215+5135, PSR J0740+6620, 4U 1702-429, and HESS J1731-347 as quark stars (QSs) within the extended quasiparticle model. In particular, our results indicate that the polytropic index $$\gamma $$ of the quark star matter becomes anisotropic with different magnetic field orientation distributions, and $$\gamma $$ decreases with the increment of the maximum star mass of QSs at zero temperature or under the density-dependent magnetic fields within quasiparticle model.

China

Peng-Cheng Chu

He Liu

Hong-Ming Liu

Min Ju

Xu-Hao Wu

Ying Zhou

Xiao-Hua Li

Quark star matter within an extended quasiparticle model

We investigate the properties of hybrid star and the mixed phase core to explore the radius ratio of the mixed phase in hybrid star. In the context of observed massive neutron stars (NSs), we examine the internal structure, phase transitions, and the impacts of the equation of state (EOS) in maximum hybrid star. We investigate the stiffness changes in the EOS during the hadron-quark phase transition within the hybrid stars. The relativistic mean-field (RMF) model is used to describe hadronic matter, while to the represent quark matter, the Nambu–Jona–Lasinio (NJL) model is applied. We explore the strength of vector coupling in quark matter, which delays the onset density of the mixed phase and reduces the size of the mixed-phase core in a hybrid star, but does not exhibit a clear correlation with the central density. In a hybrid star with a maximum mass of approximately 2 solar masses ( $$M_\odot $$ ), a mixed-phase core of $$\sim $$ 5 km may exist, comprising about $$40\%$$ of the total radius. However, our results do not support the existence of a sizable quark core containing the mixed phase ( $$R_\mathrm{{MP}}>1/2~R_\mathrm{{total}}$$ ) for the maximum-mass hybrid star or for a 2 $$M_\odot $$ massive star.

Xuhao Wu

The mixed phase quark core in massive hybrid stars

Abstract In this study, we examine the impact of the gluon condensate on holographic entanglement entropy within an Einstein-Dilaton model at both zero and finite temperatures. A critical length exists for the difference in entanglement entropy between connected and disconnected surfaces in this model, which is typically interpreted as an indicator of phase transition. As the gluon condensate increases, the critical length decreases, suggesting that confinement strengthens at zero temperature. Additionally, the entropic C-function abruptly drops to zero at the critical length, indicating the absence of entangled states. At finite temperatures, the results show that the effect of the gluon condensate on the critical length is qualitatively similar to that at zero temperature. We observe that the entropic C-function increases as a function of L at finite temperature, though it exhibits competitive behaviors when the gluon condensate is large.

Xun Chen

Bo Yu

Mitsutoshi Fujita

The Effect of Gluon Condensate on the Entanglement Entropy in a Holographic Model

We investigate the speed of sound and polytropic index of quantum chromodynamics (QCD) matter in the full phase diagram based on a three-flavor Polyakov-looped Nambu-Jona-Lasinio (PNJL) model. The speed of sound and polytropic index in isothermal and adiabatic cases all have a dip structure at the low chemical potential side of the chiral phase transition boundary, and these quantities reach their global minimum values at the critical end point (CEP) but are not completely zero, where the values in adiabatic are lightly greater than those in isothermal. Different from the speed of sound, the polytropic index rapidly form a peak after crossing the chiral phase transition boundary, which is observed for the first time. Along the hypothetical chemical freeze-out lines, the speed of sound rapidly decreases near the CEP, followed by a small spinodal behavior, while the polytropic index, especially in isothermal, exhibits a more pronounced and nearly close to zero dip structure as it approaches the CEP.

Yong-Hang Yang

Chi Yuan

Speed of sound and polytropic index in the Polyakov-loop Nambu-Jona-Lasinio model

We investigate the thermodynamical properties of color-flavor locked (CFL) quark matter at zero temperature, finite temperature, and strong magnetic field by using quasiparticle model. We find that considering CFL quark phase can significantly change the equation of state (EOS) as well as the properties of quark matter in quark stars (QSs) at finite temperature or under magnetic field within quasiparticle model. In particular, our results have shown that we can provide the large QSs within CFL quark phase from quasiparticle model by satisfying both the upper limit of  $$\Lambda _{1.4}&lt;800$$  <math> <mrow> <msub> <mi>Λ</mi> <mrow> <mn>1.4</mn> </mrow> </msub> <mo>&lt;</mo> <mn>800</mn> </mrow> </math>   for the low-spin priors of 1.4 solar mass pulsars from GW170817 and the new estimates of the mass-radius region from PSR J0740 + 6620, PSR J0030 + 0451, HESS J1731-347, and 4U 1702-429, which cannot be obtained by considering the QSs with SQM within quasiparticle model.

Qian Cao

Properties of color-flavor locked matter in a quasiparticle model

Using gauge/gravity duality, we investigate the string breaking and dissolution of two heavy quarks coupled to a light quark at finite temperature. It is found that three configurations of QQqexist with the increase in separation distance for heavy quarks in the confined phase. Furthermore, string breaking occurs at the distance   $ L_{QQq} = 1.27\; {\rm{fm}} $   (   $ L_{QQq} = 1.27\; {\rm{fm}} $  ) for the decay mode   $ L_{QQq} = 1.27\; {\rm{fm}} $  . In the deconfined phase, QQq melts at a certain distance and then becomes free quarks. Finally, we compare the potential of QQq with that of   $ L_{QQq} = 1.27\; {\rm{fm}} $  , and it is found that   $ L_{QQq} = 1.27\; {\rm{fm}} $   is more stable than QQqat high temperatures.

Xiao-hua Li

Studying the potential of At Finite Temperature in a Holographic Model  

We study the thermodynamic properties of asymmetric quark matter, large mass quark stars (QSs), and proto-quark stars (PQSs) within the quasiparticle model. Considering the effects of temperature within quasiparticle model can significantly influence the EOS and the entropy of strange quark matter (SQM), quark fractions in SQM, as well as the tidal deformability and the maximum mass of PQSs along the star evolution line. Our results indicate that the recent discovered heavy compact stars PSR J0348+0432, MSR J0740+6620, PSR J2215+5135, and especially the GW190814’s secondary component  $$m_2$$  <math> <msub> <mi>m</mi> <mn>2</mn> </msub> </math>   can be well described as QSs within the quasiparticle model. The tidal deformability for the QSs describing the heavy compact stars is extremely large, which can not well describe GW170817 as QSs, and the effects of the temperature in the heating process along the star evolution will further increase the tidal deformability and the maximum mass of PQSs.

Yao-Yao Jiang

Zhen Zhang

Xiao-Min Zhang

Quark star matter at finite temperature in a quasiparticle model

We study the thermodynamic properties of asymmetric quark matter and large mass quark stars within the confined-isospin-density-dependent-quark-mass model. We find that the quark matter symmetry energy should be very large in order to describe the recent discovered heavy compact stars PSR J0348+0432 ( $$\text {2.01}\pm \text {0.04}M_{\odot }$$  <math> <mrow> <mtext>2.01</mtext> <mo>±</mo> <mtext>0.04</mtext> <msub> <mi>M</mi> <mo>⊙</mo> </msub> </mrow> </math>  ), MSP J0740+6620 ( $$\text {2.14}\pm ^\text {0.10}_\text {0.09}M_{\odot }$$  <math> <mrow> <mtext>2.14</mtext> <msubsup> <mo>±</mo> <mtext>0.09</mtext> <mtext>0.10</mtext> </msubsup> <msub> <mi>M</mi> <mo>⊙</mo> </msub> </mrow> </math>   of 68.3 $$\%$$  <math> <mo>%</mo> </math>   credibility interval and  $$\text {2.14}\pm ^\text {0.20}_\text {0.18}M_{\odot }$$  <math> <mrow> <mtext>2.14</mtext> <msubsup> <mo>±</mo> <mtext>0.18</mtext> <mtext>0.20</mtext> </msubsup> <msub> <mi>M</mi> <mo>⊙</mo> </msub> </mrow> </math>   of 95.4 $$\%$$  <math> <mo>%</mo> </math>   credibility interval) and PSR J2215+5135 (2.27 $$\pm ^\text {0.10}_\text {0.09}M_{\odot }$$  <math> <mrow> <msubsup> <mo>±</mo> <mtext>0.09</mtext> <mtext>0.10</mtext> </msubsup> <msub> <mi>M</mi> <mo>⊙</mo> </msub> </mrow> </math>  ) as QSs. The tidal deformability  $$\Lambda _{1.4}$$  <math> <msub> <mi>Λ</mi> <mrow> <mn>1.4</mn> </mrow> </msub> </math>   of the QSs is also investigated in this work, and the result indicates that  $$\Lambda _{1.4}$$  <math> <msub> <mi>Λ</mi> <mrow> <mn>1.4</mn> </mrow> </msub> </math>   may depend on the isospin effects and the strength / orientation distribution of the magnetic fields inside the quark stars.

Yi Zhou

Hong-Yang Ma

Quark star matter in heavy quark stars

We study the properties of strange quark matter (SQM) and quark stars (QSs) in strong magnetic fields within the extended confined isospin-density-dependent mass (CIDDM) model including the temperature dependence of the equivalent mass for quarks. The quark symmetry energy, quark symmetry free energy, and the equation of state (EOS) of SQM in constant magnetic fields at finite temperature are investigated, and it is found that including the temperature dependence in CIDDM model and considering strong magnetic fields can both significantly influence the properties of the SQM and the maximum mass of quark stars. Using the density-dependent magnetic field and assuming two extreme cases for the magnetic field orientation in QSs (the radial orientation in which the local magnetic fields are along the radial direction and the transverse orientation in which the local magnetic fields are randomly oriented but perpendicular to the radial orientation), we analyze the mass-radius relations for different stages of the protoquark stars (PQSs) along the star evolution. Our results indicate that the maximum mass of magnetized PQSs may depend on not only the strength distribution and the orientation of the magnetic fields inside the PQSs, but also the heating process and the cooling process in the star evolution.

Bin Wang

Yu-Min Dong

Quark matter and quark stars in strong magnetic fields at finite temperature within the confined-isospin-density-dependent mass model

We extend the SU(3) Nambu–Jona-Lasinio (NJL) model to include two types of vector interaction. Using these two types of vector interaction in NJL model, we study the quark symmetry free energy in asymmetric quark matter, the constituent quark mass, the quark fraction, the equation of state (EOS) for β -equilibrium quark matter, the maximum mass of QSs at finite temperature, the maximum mass of proto-quark stars (PQSs) along the star evolution, and the effects of the vector interaction on the QCD phase diagram. We find that comparing zero temperature case, the values of quark matter symmetry free energy get larger with temperature increasing, which will reduce the difference between the fraction of u , d and s quarks and stiffen the EoS for β -equilibrium quark matter. In particular, our results indicate that the maximum masses of the quark stars increase with temperature because of the effects of the quark matter symmetry free energy, and we find that the heating(cooling) process for PQSs will increase (decrease) the maximum mass within NJL model.