arXiv subjects

Sheng-Qin Feng

Publications and source records attributed to Sheng-Qin Feng.

At least 19 recordsLinked to original sources

arXiv2026

Causality and Stability of First-Order Relativistic Spin Hydrodynamics with Conserved Charges

We study the causality and stability of first-order relativistic spin hydrodynamics with particle-number conservation. By deriving the complete dispersion relations of linear perturbations around global equilibrium, we find that conserved-charge dynamics modifies the sound sector and introduces additional non-hydrodynamic modes absent in the charge-neutral theory. While the structure of spin relaxation modes remains unchanged, the stability conditions acquire new contributions from charge diffusion and thermodynamic susceptibilities. More importantly, a particle-number-induced mode is shown to violate the causality condition in the short-wavelength limit. We further demonstrate that particle-number conservation does not remove the instability inherent in first-order spin hydrodynamics. These results reveal nontrivial interplay between spin and conserved-charge dynamics and provide important constraints on relativistic spin hydrodynamic theories at finite density.

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arXiv2026

Chiral Phase Transition in Rotating Quark Matter with Chiral Imbalance: A Medium Separation Scheme Regularized NJL Model Study

We investigate the chiral phase transition in rotating quark matter with chiral imbalance using the two-flavor Nambu-Jona-Lasinio (NJL) model regularized by the Medium Separation Scheme (MSS). Our numerical calculations demonstrate that the chiral chemical potential $\mu_5$ and angular velocity $\omega$ exert opposite effects on chiral symmetry breaking: $\mu_5$ enhances the breaking, raising the pseudocritical temperature $T_{pc}$ and sharpening the phase transition, while $\omega$ suppresses the breaking, lowering $T_{pc}$ and smearing the transition. Notably, chiral imbalance buffers the rotation-induced softening of the phase transition-the suppression of $T_{pc}$ by $\omega$ weakens progressively as $\mu_5$ increases. The MSS predicts a monotonic increase of $T_{pc}$ with $\mu_5$, in qualitative agreement with LQCD, resolving the discrepancy found in traditional regularization. Furthermore, the rotational suppression of $T_{pc}$ exhibits strong radius dependence: larger rotation radii amplify the suppression due to enhanced spacetime curvature and centrifugal effects, and can even induce an abrupt drop in $T_{pc}$ in the high-rotation region. These findings clarify the interplay between rotation and chiral imbalance in modulating the QCD chiral phase transition and validate the MSS as a reliable regularization framework for such extreme systems.

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arXiv2026

Causality and stability analysis of relativistic spin hydrodynamics: Insights from a nonvanishing spin density background

We investigate the stability and causality of relativistic spin hydrodynamics in the presence of a nonvanishing spin density background, assuming that the spin chemical potential $\omega^{\mu\nu}$ is of leading order ($\omega^{\mu\nu} \sim \mathcal{O}(1)$) in the gradient expansion and is treated as a finite background in the linear perturbation analysis. It is found that within the first-order spin hydrodynamic framework, a finite spin density background modifies the dispersion relations, and modes propagating along different directions are controlled by distinct transport coefficients. Certain specific modes only appear in the $x$ direction. However, the modes in the large wave-vector limit exhibit acausal behavior. To address this issue, we subsequently adopt the framework of minimal causal spin hydrodynamics and derive the corresponding stability and causality conditions. The spin density background directly determines whether stability and causality can be satisfied simultaneously. In the small wave-vector limit, the results are similar to those of the first-order theory. In the large wave-vector region, however, significant differences emerge: the distinctions between different directions are no longer merely simple substitutions of transport coefficients, but involve more complex combinations. This indicates that the difference between modes in different directions increases with increasing wave vector.

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arXiv2026

Spectral Signatures of Heavy Quarkonia in a Rotating and Anisotropic Quark-Gluon Plasma: A Holographic Study

We investigate the in-medium spectral functions and effective masses of heavy quarkonia charmonium ($J/Ψ$) and bottomonium ($Υ(1S)$) in a quark-gluon plasma (QGP) possessing both global rotation and spatial anisotropy. Using a gauge/gravity holographic model incorporating finite temperature, chemical potential, and warp factor, we compute the spectral signatures non-perturbatively. Our results show that both rotation and anisotropy enhance quarkonium dissociation, manifesting as peak suppression and width broadening in the spectral functions. Crucially, their effects are directional: anisotropy primarily dissociates longitudinally polarized states, while rotation more strongly disrupts transversely polarized ones. A competitive interplay exists: for small anisotropy, rotational effects dominate at high angular velocity, whereas for large anisotropy, anisotropy governs the dissociation regardless of rotation strength. Furthermore, rotation induces a non-monotonic temperature dependence in the transverse effective mass of $J/Ψ$, while strong anisotropy causes similar non-monotonicity in the longitudinal effective mass of $J/Ψ$. These findings reveal how the distinct symmetry breaking patterns induced by QGP rotation and anisotropy reshape the heavy quarkonium spectrum, providing new insights into polarization-dependent suppression in non-central heavy-ion collisions.

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arXiv2025

Non-extensive NJL model study of QCD phase structure with chiral imbalance and strong magnetic fields

Based on the two-flavor NJL model with Tsallis non-extensive statistics, this work explores the QCD phase structure and thermodynamic properties under strong magnetic fields and chiral imbalance. The Tsallis parameter $q$ captures non-equilibrium effects relevant to heavy-ion collisions. Key findings reveal that the critical temperature $T_c$ decreases with increasing $q$, indicating that non-equilibrium conditions promote chiral symmetry restoration at lower temperatures. The chiral chemical potential $\mu_5 $ significantly alters the magnetic response, with a transition from magnetic catalysis to inverse magnetic catalysis under certain conditions. For $q > 1$, non-monotonic behavior of $T_c$ with magnetic field $eB$ emerges. Pressure becomes anisotropic under strong $eB$, and the speed of sound exhibits a dip near $T_c$, shifting to lower temperatures with larger $q$. These results highlight how non-extensive statistics, chiral imbalance, and magnetic fields collectively influence the QCD phase diagram and thermodynamic observables, offering insights for interpreting heavy-ion collision data.

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arXiv2025

Quark anomalous magnetic moments and neutral pseudoscalar meson dynamics with three-flavor NJL model in magnetized quark matter

We investigate the influence of quark anomalous magnetic moments (AMMs) on the mass spectra of neutral pseudoscalar mesons ($π$, $K$, $η$, $η^{'}$) under external magnetic fields, finite temperatures, and quark chemical potentials using the three-flavor Nambu-Jona-Lasinio model. By incorporating AMMs at the quark level, we reveal that AMMs significantly alter the magnetic field dependence of constituent quark masses, inducing first-order phase transitions for light quarks at critical fields, while strange quarks exhibit nonmonotonic mass behavior. The inclusion of AMMs reshapes the QCD phase diagram, suppressing chiral transition temperatures, and the strong magnetic field shifts critical endpoints toward lower $μ$ and higher $T$ without AMMs. The crossover phase transition without AMMs is replaced by a first-order transition with AMMs under strong fields. Moreover, the inverse magnetic catalysis (IMC) induced by the introduction of AMMs qualitatively aligns with the predictions of lattice QCD (LQCD) for the dependence of phase transition temperature on the magnetic field. For mesons, a larger AMM triggers abrupt mass collapses and enhances flavor spitting at zero $μ$ and $T$ and accelerates chiral restoration for $K$ and $η$ mesons via thresholds tied to strange quark masses in finite $μ$ and $T$. These findings underscore AMMs' critical role in reconciling effective model predictions with LQCD results, particularly in reproducing IMC and explaining phase transition dynamics.

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arXiv2025

Magnetodynamic Characteristics and QGP Energy Dissipation in RMHD Framework with Relativistic Heavy-Ion Collisions

Relativistic heavy-ion collisions generate ultra-strong magnetic fields that interact with the quark-gluon plasma (QGP), a key focus of high-energy physics research.This study investigates QGP energy density evolution under time-dependent magnetic fields within a (1 +1)D relativistic magnetohydrodynamic (RMHD) framework integrated with Bjorken flow. Three magnetic field temporal evolution models (Type-1,Type-2,Type-3) are analyzed for two different equations of state: (1) $p = c_s^2 e$, and (2)$p = c_s^2 e-2MB$ incorporating a temperature-dependent magnetic susceptibility derived from lattice QCD. Results show that stronger magnetic fields consistently suppress QGP energy density decay,with suppression magnitude dependent on the magnetic field's temporal profile. Ultra-relativistic fluids exhibit slowed energy decay due to magnetic pressure counteracting hydrodynamic expansion.In contrast,magnetized conformal fluids display faster energy dissipation under identical conditions, arising from the synergistic effect of enhanced magnetic fluid coupling,increased energy dissipation during interaction,and QGP's perfect fluid expansion at elevated temperatures.Temperature-dependent magnetic susceptibility reveals a transition from diamagnetic (confined phase) to paramagnetic (deconfined QGP phase) behavior, introducing a feedback mechanism that strengthens energy retention at higher temperatures. This work clarifies the interplay between magnetic field dynamics,QCD phase structure, and hydrodynamic expansion, providing key observational signatures for distinguishing fluid types in heavy-ion collisions and advancing realistic modeling of magnetized QGP.

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arXiv2025

Chiral phase transition and spin alignment of vector mesons with chiral imbalance in a rotating QCD medium

We study the two-flavor NJL model under the rotation and chiral chemical potential $μ_{5}$. Firstly, the influence of chiral imbalance on the chiral phase transition in the $T_{pc}-ω$ plane is investigated. Research manifests that as $μ_{5}$ increases, the critical point (CEP) of the $T_{pc}-ω$ plane chiral phase transition will move closer to the $T$ axis. This means that the chiral chemical potential $μ_{5}$ can significantly affect the $T_{pc}-ω$ phase diagram and phase transition behavior. While discussing the $T_{pc}-ω$ phase diagram, we also study the spin alignment of the $ρ$ vector meson under rotation. In the study of the spin alignment of the vector meson $ρ$, $ρ_{00}$ is the $00$ element of the spin density matrix of vector mesons. At high temperatures, $ρ_{00}$ is close to $1/3$, it indicates that the spin alignment of the vector meson $ρ$ is isotropic. It is found that increasing the chiral chemical potential $μ_{5}$ significantly enhances $ρ_{00}$, and makes $ρ_{00}$ approaching to $1/3$ around the phase transition temperature. When rotational angular velocity is zero, $ρ_{00}$ is close to $1/3$, but as $ω$ increases, $ρ_{00}$ significantly decreases, and deviates $1/3$, indicating that rotation can significantly cause polarization characteristics. The $ρ_{00}-r$ relationship near the phase transition temperature is studied. It is found that the farther away from the center of rotation, the lower the degree of spin polarization of the system. It is also found that the influence of chiral imbalance on the $ρ_{00}-r$ relationship is also significant.

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arXiv2024

Rotation effect on the spectral function of heavy vector mesons in holographic QCD

Exploring heavy vector mesons of the $ J / ψ$ and $ Υ( 1 S )$ is crucial for understanding the quark gluon plasma (QGP) formed in heavy ion collisions. The influences of rotational effect on the properties of the $ J / ψ$ and the $ Υ( 1 S )$ are investigated by incorporating rotation medium into the holographic QCD. It is found that temperature, chemical potential, and rotational radius effects enhance the dissociation process of the $ J / ψ$ and the $ Υ( 1 S )$ states within the medium. This rotation-induced effect is more significant for heavy vector mesons in the transverse direction than that of the longitudinal direction. The first holographic study on the influence of the radius of a homogeneous rotating system on the vector meson spectrum is proposed. It is found that increasing in rotation radius promotes the dissociation of vector mesons of the $ J / ψ$ and $ Υ( 1 S )$. We also find that the dissociation perpendicular to the direction of rotational angular velocity is more significant than that parallel to it at large rational radius.

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arXiv2024

Effects of tensor spin polarization on the chiral restoration and deconfinement phase transitions

Effects of tensor spin polarization (TSP) on the chiral restoration and deconfinement phase transitions are studied in Polyakov loop extended Nambu-Jona-Lasinio (PNJL) model. For chiral phase transition, the higher the polarized degree of quark-antiquark pairs under the strong magnetic field, the higher the phase transition temperature. The TSP corrects the position of the critical end point. The small impact of TSP on the phase transition temperature is found for the deconfinement phase transition. On the other hand, we divide the phase space into three ranges based on the phase diagram obtained from the PNJL model: the confinement phase with chiral symmetry broken, the deconfinement phase with restored chiral symmetry, and the confinement phase with restored chiral symmetry (quarkyonic phase). It is found that TSP has only a very small effect on the anisotropic pressure in the deconfined phase with chiral symmetry restored and the quarkyonic phase, but it has a very strong effect on the anisotropic pressure in the confined phase with chiral symmetry broken. This is because TSP is closely related to chiral symmetry. The restoration of chiral symmetry means the dissociation of spin polarization condensate.

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arXiv2024

Rotation effect on the deconfinement phase transition in holographic QCD

The impact of rotation on the deconfinement phase transition under the EM system of the soft and the hard wall models in holographic QCD is studied in this paper. The metric by cylindrical coordinates with rotation is introduced into the system to calculate the Hawking temperature. The first holographic study on the influence of the radius of a homogeneous rotating system on the phase diagram is proposed. It is found that the phase transition temperature hardly changes with the rotation angular velocity for a small rotation radius. Only with a larger rotation radius can the change in rotational angular velocity significantly alter the phase transition temperature. The phase transition temperature decreases rapidly with the increase of rotation angular velocity as the rotation radius increases.

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arXiv2023

Shear viscosity coefficient of magnetized QCD medium with anomalous magnetic moments near chiral phase transition

We study the properties of the shear viscosity coefficient of quark matter near the chiral phase transition at finite temperature and chemical potential, and the kinds of high temperature, high density and strong magnetic field background. The strong magnetic field induces anisotropy, that is, the quantization of Landau energy levels in phase space. If the magnetic field is strong enough, it will interfere with significant QCD phenomena, such as the generation of dynamic quark mass, which may affect the transport properties of quark matter. The inclusion of the anomalous magnetic moments of the quarks at finite density into the Nambu-Jona-Lasinio model gives rise to additional spin polarization magnetic effects. It is found that both the ratio $η/s$ of shear viscosity coefficient to entropy and the collision relaxation time $τ$ show similar trend with temperature, both of which reach minima around the critical temperature. The shear viscosity coefficient of the dissipative fluid system can be decomposed into five different components as the strong magnetic field exists. The influences of the order of chiral phase transition and the critical end point on dissipative phenomena in such a magnetized medium are quantitatively investigated. It is found that $η_{1}$, $η_{2}$, $η_{3}$, and $η_{4}$ all increase with temperature. For first-order phase transitions, $η_{1}$, $η_{2}$, $η_{3}$, and $η_{4}$ exhibit discontinuous characteristics.

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arXiv2023

Spin Polarization and Anomalous Magnetic Moment in a (2 + 1)-flavor Nambu-Jona-Lasinio model in a thermomagnetic background

We investigate the magnetized QCD matter and chiral phase transition in a (2 þ 1)-flavor Nambu-Jona-Lasinio (NJL) model at finite temperature and chemical potential by comparing the contributions from the tensor spin polarization (TSP) and anomalous magnetic moment (AMM) of quarks. For light u and d quarks, when TSP and AMM are not considered, the magnetized system is characterized by magnetic catalysis. The introduction of TSP will further enhance the magnetic catalytic characteristics. On the other hand, when AMM is introduced, the phase-transition temperature decreases with the magnetic field, which is the feature of inverse magnetic catalysis. The phase diagram of u and d quarks will change from the crossover phase transition to the first order phase transition with the increase of magnetic field and chemical potential when AMM is induced. The phase diagram will not change from the crossover phase transition to the first-order phase transition when TSP is induced. For the phase diagram of strange s quark, whether TSP or AMM is induced, the phase diagram will keep a crossover phase transition with the increase of magnetic field and chemical potential.

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arXiv2023

Shear viscosity coefficient of magnetized QCD medium near chiral phase transition

We study the properties of the shear viscosity coefficient of quark matter at finite temperature and chemical potential near chiral phase transition in a strong background magnetic field. A strong magnetic field induces anisotropic features, phase-space Landau-level quantization, and if the magnetic field is sufficiently strong, interferes with prominent QCD phenomena such as dynamical quark mass generation, likely affecting the quark matter transport characteristics. The modified Nambu-Jona-Lasinio (NJL) model with inverse magnetic catalysis effect by fitting the Lattice QCD (LQCD) results is used to calculate the changes of quasiparticle related thermodynamic quantities, and the shear viscosity of the system medium, which is analyzed under the relaxation time approximation. We quantify the influence of the order of chiral phase transition and the critical endpoint on dissipative phenomena in such a magnetized medium. When the magnetic field exists, the shear viscosity coefficient of the dissipative fluid system can be decomposed into five different components. In strong field limit, we make a detailed study of the dependencies of $η_{2}$ and $η_{4}$ on temperature and magnetic field for the first order phase transition and critical endpoint transition. respectively. It is found that $η_{2}$ and $η_{4}$ both decrease with magnetic field and increase with temperature, and the discontinuities of $η_{2}$ and $η_{4}$ occur at the first order phase transition point.

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arXiv2022

Holographic deconfined QGP phase diagram and entropy with an anomalous flow in a magnetic field background

We assume that the initial hydrodynamic environment is a Quark Gluon Plasma (QGP) phase where merely u and d quarks are considered when adding a magnetic field. When considering the chiral magnetic effect in relativistic heavy ion collisions, an anomalous current will be formed in the QGP environment. The chiral magnetic current formed by these u and d quarks has an impact on the heavy quarkonium. By using fluid/gravity duality, the metric with anomalous flow is established by using fluid/gravity duality, so as to introduce the magnetic field effect into the corresponding metric. And then we use heavy quarkonium as a probe to study phase transition, and utilize the effective string tension of the heavy quarkonium to study phase transition by AdS/QCD theory. The characteristics of reporting inverse magnetic catalysis for the confinement-deconfinement transition with anomalous flow are in qualitative agreement with lattice QCD findings. The heavy-quarkonium asymptotic entropy distributions with different magnetic field around the confinement-deconfinement transition temperature are given in the paper.

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arXiv2019

A systematical study of the chiral magnetic effects at the RHIC and LHC energies

Considering the magnetic field response of the QGP medium, we perform a systematical study of the chiral magnetic effect(CME), and make a comparison it with the experimental results for the background-subtracted correlator $H$ at the energies of the RHIC Beam Energy Scan (BES) and LHC energy. The CME signals from our computations show a centrality trend and beam energy dependence that are qualitatively consistent with the experimental measurements of the charge dependent correlations. The time evolution of the chiral electromagnetic current at the RHIC and LHC energies is systematically studied. The dependence of the time-integrated current signal on the beam energy $\sqrt{s}$ with different centralities is investigated. Our phenomenological analysis shows that the time-integrated electromagnetic current is maximal near the collision energy $\sqrt{s} \approx 39$ GeV. The qualitative trend of the induced electromagnetic current is in agreement with the CME experimental results at the RHIC and LHC energies.

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arXiv2019

A systematically study of thermal width of heavy quarkonia in a finite temperature magnetized background from holography

By simulating the finite temperatures magnetized background in the RHIC and LHC energies, we systematically study the characteristics of thermal widths and potentials of heavy quarkonia. It is found that the magnetic field has less influence on the real potential, but has a significant influence on the imaginary potential, especially in the low deconfined temperature. Extracted from the effect of thermal worldsheet fluctuations about the classical configuration, the thermal width of $Υ(1s)$ in the finite temperature magnetized background is investigated. It is found that at the low deconfined temperature the magnetic field can generate a significant thermal fluctuation of the thermal width of $Υ(1s)$, but with the increase of temperature, the effect of magnetic field on the thermal width becomes less important, which means the effect of high temperature completely exceeds that of magnetic field and magnetic field become less important at high temperature. The thermal width decreases with the increasing rapidity at the finite temperature magnetized background. It is also observed that the effect of the magnetic field on the thermal width when dipole moving parallel to the magnetic field direction are larger than that moving perpendicular to the magnetic field direction, which implies that the magnetic field tends to enhance thermal fluctuation when dipole moving parallel to the direction of magnetic field. The thermal width of $Υ(1S)$ hardly changes with the increasing temperature when dipole moving perpendicular to the magnetic field. But when dipole moving parallel to the magnetic field, the thermal width at low temperature is obviously larger than that at high temperature.

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arXiv2019

Energy loss of heavy and light quarks in holographic magnetized background

We systematically study holographic effects on the magnetic field dependence of the drag force, diffusion coefficient, jet quenching parameter of heavy quarks and the shooting string energy loss of light quarks in the RHIC and LHC energy regions by using the AdS/CFT correspondence in this paper. This study is motivated by the phenomena of strong magnetic field and jet quenching, which have been found in relativistic heavy ion collisions. The probe's direction of motion is perpendicular and parallel to the direction of magnetic field $B$. The effects of magnetic field on energy loss when moving perpendicular to the magnetic field direction are larger than moving parallel to the magnetic field direction, which implies that the magnetic field tends to suppress more quarks and jets when moving in the transverse direction than in the parallel direction. It is found that the diffusion coefficient decreases with the magnetic field in the transverse direction, but increases with the magnetic field in the parallel direction, which indicates that the quark may diffuse farther when moving parallel to the magnetic field direction. We also find that the magnetic field will enhance the energy loss of the light quarks when moving in the transverse direction than in the parallel direction.

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