arXiv subjects

He-Xia Zhang

Publications and source records attributed to He-Xia Zhang.

8 recordsLinked to original sources

arXiv2025

System-size dependence of $γ$-jet modifications in heavy-ion collisions

Medium modifications of the $γ$-triggered jets are investigated with the Linear Boltzmann Transport (LBT) model in heavy-ion collisions with varying system sizes, focusing on centrality dependence in Pb+Pb and Xe+Xe collisions at the LHC. Our numerical results reveal that jets produced in central collisions exhibit a wider transverse asymmetry ($A_N^y$) distribution, a broader jet shape, and a more pronounced $γ$-jet transverse momentum imbalance ($X_{Jγ}=p_T^{\rm jet}/p_T^γ$) compared to peripheral collisions. These effects arise from the longer path length and stronger jet-medium interactions in central collisions, leading to enhanced jet quenching and medium response. Our findings demonstrate that the magnitude of $γ$-jet modifications is sensitive to the size and centrality of the collision system, with larger systems inducing more significant alterations due to increased energy loss and medium feedback.

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arXiv2024

Non-extensive Hard Thermal Loop Resummation and Its Applications: Analysis in Zero and Finite Magnetic Fields

The impact of non-extensive statistics on the hard thermal loop (HTL) resummation technique is investigated, in the absence and presence of a magnetic field. By utilizing the non-extensive bare propagators in the real-time formalism of finite temperature field theory, we determine the non-extensive deformations of both HTL gluon self-energies and resummed gluon propagators at the one-loop order. We observe that the introduction of non-extensivity results in distinct shifts in the Debye masses for the retarded/advanced and symmetric gluon self-energies. Applying the non-extensive modified resummed gluon propagators to obtain the dielectric permittivity of a quark-gluon plasma (QGP), we thereby derive the static heavy quark potential, which incorporates both short-range Yukawa and long-range string-like interactions between heavy quarks and the QGP medium. The real part of the potential exhibits increased screening as the non-extensive parameter $q$ ($q \geq 1$) increases, reducing the binding energies of heavy quarkonia. Furthermore, including non-extensivity enhances the magnitude of the imaginary part of the potential, causing a broadening in the decay widths of heavy quarkonia. Based on these observations, we estimate the melting temperatures of heavy quarkonia. Our results indicate that non-extensivity lowers the melting temperatures of heavy quarkonia, thus facilitating their dissociation, whereas the presence of a magnetic field inhibits this dissociation.

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arXiv2024

Impact of (magneto-)thermoelectric effect on diffusion of conserved charges in hot and dense hadronic matter

We investigate the thermoelectric effect, which describes the generation of an electric field induced by temperature and conserved charge chemical potential gradients, in the hot and dense hadronic matter created in heavy-ion collisions. Utilizing the Boltzmann kinetic theory within the repulsive mean-field hadron resonance gas model, we evaluate both the diffusion thermopower matrix and diffusion coefficient matrix for the baryon number ($B$), electric charge ($Q$), and strangeness ($S$). The Landau-Lifshitz choice for the rest frame of the fluid is enforced in the derivation. We find that the thermoelectric effect hinders the diffusion processes of multiple conserved charges, particularly reducing the coupling between electric charge and baryon number (strangeness) in baryon (strangeness) diffusion. Given that the repulsive mean-field interactions between hadrons have a significant effect on the diffusion thermopower matrix and diffusion coefficient matrix in the baryon-rich region, we extend the investigation to include the impact of magnetic fields, analyzing the magneto-thermoelectric effect on both the diffusion coefficient matrix and the Hall-like diffusion coefficient matrix. The sensitivities of the magnetic field-dependent diffusion thermopower matrix and magneto-thermoelectric modified diffusion coefficient matrix to the choices of various transverse conditions are also studied.

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arXiv2024

Responses of quark-antiquark interaction and heavy quark dynamics to magnetic field

We investigate the impact of the magnetic field generated by colliding nuclei on heavy quark-antiquark interactions and heavy quark dynamics in the quark-gluon plasma (QGP). By means of hard-thermal-loop resummation technique combined with dimension-two gluon condensates, the static heavy quark potential and heavy quark momentum diffusion coefficient, which incorporate both perturbative and non-perturbative interactions between heavy quarks and the QGP medium, are computed beyond the lowest Landau level approximation. We find that the imaginary part of the heavy quark potential in the magnetic field exhibits significant anisotropy. Specifically, the absolute value of the imaginary part is larger when the quark-antiquark separation is aligned perpendicular to the magnetic field direction, compared to when it is aligned parallel to the magnetic field direction. The heavy quark momentum diffusion coefficient in the magnetized QGP medium also becomes anisotropic. As the temperature rises, the influence of higher Landau levels becomes increasingly significant, resulting in a decrease in the anisotropy ratio of the heavy quark momentum diffusion coefficient to values even below 1. At sufficiently high temperatures, this ratio ultimately approaches 1. The non-perturbative interactions are indispensable for understanding heavy quark dynamics in the low-temperature region. We also study the response of viscous quark matter to the magnetic field and explore its implications for heavy quark potential, thermal decay widths of quarkonium states, as well as heavy quark momentum diffusion coefficient.

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arXiv2022

Phenomenological study of the anisotropic quark matter in the 2-flavor Nambu-Jona-Lasinio model

With the two flavor Nambu-Jona-Lasinio (NJL) model we carry out a phenomenological study on the chiral phase structure, mesonic properties and transport properties in a momentum-space anisotropic quark matter. To calculate transport coefficients we have utilized the kinetic theory in the relaxation time approximation, where the momentum anisotropy is embedded in the estimation of both distribution function and the relaxation time. It is shown that an increase of the anisotropy parameter $ξ$ may results in a catalysis of chiral symmetry breaking. The critical endpoint (CEP) is shifted to smaller temperatures and larger quark chemical potentials as $ξ$ increases, the impact of momentum anisotropy on temperature of CEP is almost the same as that on the quark chemical potential of CEP. The meson masses and the associated decay widths also exhibit a significant $ξ$ dependence. It is observed that the temperature behavior of scaled shear viscosity $η/T^3$ and scaled electrical conductivity $σ_{el}/T$ exhibit a similar dip structure, with the minima of both $η/T^3$ and $σ_{el}/T$ shifting toward higher temperatures with increasing $ξ$. Furthermore, we demonstrate that the Seebeck coefficient $S$ decreases when temperature goes up and its sign is positive, indicating the dominant carriers for converting the temperature gradient to the electric field are up-quarks. The Seebeck coefficient $S$ is significantly enhanced with a large $ξ$ for the temperature below the critical temperature.

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arXiv2021

Effect of momentum anisotropy on quark matter in the quark-meson model

We investigate the chiral phase structure of quark matter with spheroidal momentum-space anisotropy specified by one anisotropy parameter $ξ$ in the 2+1 flavor quark-meson model. We find that the chiral phase diagram and the location of the critical endpoint (CEP) are affected significantly by the value of $ξ$. With the increase of $ξ$, the CEP is shifted to smaller temperatures and larger quark chemical potentials. And the temperature of the CEP is more sensitive to the anisotropy parameter than the corresponding quark chemical potential, which is opposite to the study for finite system volume effect. Furthermore, the effects of momentum anisotropy on the thermodynamic properties and scalar (pseudoscalar) meson masses are also studied at vanishing quark chemical potential. The numerical results show that an increase of $ξ$ can hinder the restoration of chiral symmetry. We also find that shear viscosity and electrical conductivity decrease as $ξ$ grows. However, bulk viscosity exhibits a significant non-trivial behavior with $ξ$ in the entire temperature domain of interest.

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arXiv2021

Thermoelectric properties of (an-)isotropic QGP in magnetic fields

The Seebeck effect and the Nernst effect, which reflect the appearance of electric fields along $x$-axis and along $y$-axis ($E_{x}$ and $E_{y}$), respectively, induced by the thermal gradient along $x$-axis, are studied in the QGP at an external magnetic field along $z$-axis. We calculate the associated Seebeck coefficient ($S_{xx}$) and Nernst signal ($N$) using the relativistic Boltzmann equation under the relaxation time approximation. In an isotropic QGP, the influences of magnetic field ($B$) and quark chemical potential ($μ_{q}$) on these thermoelectric transport coefficients are investigated. In the presence (absence) of weak magnetic field, we find $S_{xx}$ for a fixed $μ_{q}$ is negative (positive) in sign, indicating that the dominant carriers for converting heat gradient to electric field are negatively (positively) charged quarks. The absolute value of $S_{xx}$ decreases with increasing temperature. Unlike $S_{xx}$, the sign of $N$ is independent of charge carrier type, and its thermal behavior displays a peak structure. In the presence of strong magnetic field, due to the Landau quantization of transverse motion of (anti-)quarks perpendicular to magnetic field, only the longitudinal Seebeck coefficient ($S_{zz}$) exists. Our results show that the value of $S_{zz}$ at a fixed $μ_{q}$ in the lowest Landau level (LLL) approximation always remains positive. Within the effect of high Landau levels, $S_{zz}$ exhibits a thermal structure similar to that in the LLL approximation. As the Landau level increases further, $S_{zz}$ decreases and even its sign changes from positive to negative. The computations of these thermoelectric transport coefficients are also extended to a medium with momentum-anisotropy induced by initial spatial expansion as well as strong magnetic field.

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arXiv2020

In-medium effect on the thermodynamics and transport coefficients in van der Waals hadron resonance gas

An extension of the van der Waals hadron resonance gas (VDWHRG) model which includes in-medium thermal modification of hadron masses, the TVDWHRG model, is considered in this paper. Based on the 2+1 flavor Polyakov Linear Sigma Model(PLSM) and the scaling mass rule for hadrons we obtain the temperature behavior of all hadron masses for different fixed baryon chemical potentials $μ_{B}$. We calculate various thermodynamic observables at $μ_{B}=0$ GeV in TVDWHRG model. An improved agreement with the lattice data by TVDWHRG model in the crossover region ($T\sim 0.16-0.19$ GeV) is observed as compared to those by VDWHRG and Ideal HRG (IHRG) models. We further discuss the effects of in-medium modification of hadron masses and VDW interactions on the transport coefficients such as shear viscosity ($η$), scaled thermal ($λ/T^{2}$) and electrical ($σ_{el}/T$ conductivities in IHRG model at different $μ_{B}$, by utilizing quasi-particle kinetic theory with relaxation time approximation.

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