2022年

(9) Hao-Hao Peng, Sihao Wu, Ren-jie Wang, Duan She, Shi Pu, Anomalous magnetohydrodynamics with temperature-dependent electric conductivity and application to the global polarization, Phys. Rev. D 107 (2023) 9, 096010, arXiv: 2211.11286.

 

We have derived the solutions of the relativistic anomalous magnetohydrodynamics with longitudinal Bjorken boost invariance and transverse electromagnetic fields in the presence of temperature or energy density dependent electric conductivity. We consider the equations of states in a high temperature limit or in a high chiral chemical potential limit. We obtain both perturbative analytic solutions up to the order of ℏ and numerical solutions in our configurations of initial electromagnetic fields and Bjorken flow velocity. Our results show that the temperature or energy density dependent electric conductivity play an important role to the decaying of the energy density and electromagnetic fields. We also implement our results to the splitting of global polarization for Λ and`Λ hyperons induced by the magnetic fields. Our results for the splitting of global polarization disagree with the experimental data in low energy collisions, which implies that the contribution from electromagnetic fields may be insufficient to explain the global polarization of Λ and`Λ hyperons in the low energy collisions.

 

(8) Shuo Lin, Ren-Jie Wang, Jian-Fei Wang, Hao-Jie Xu, Shi Pu, Qun Wang, Photoproduction of e⁺ e^-  in peripheral isobar collisions, Phys. Rev. D 107 (2023) 5, 054004, arXiv: 2210.05106.

We investigate the photoproduction of dielectrons in peripheral collisions of Ru+Ru and Zr+Zr at 200 GeV. With the charge and mass density distributions given by the calculation of the density functional theory, we calculate the spectra of transverse momentum, invariant mass, and azimuthal angle for dielectrons at 40–80% centrality. The ratios of these spectra in Ru+Ru collisions over to Zr+Zr collisions are shown to be smaller than (44/40)⁴ (the ratio of Z⁴ for Ru and Zr) at low transverse momentum. The deviation arises from the different mass and charge density distributions in Ru and Zr. So the photoproduction of dileptons in isobar collisions may provide a new way to probe the nuclear structure.

 

(7) Shuo Fang, Shi Pu, Di-Lun Yang, Quantum kinetic theory for dynamical spin polarization from QED-type interaction, Phys. Rev. D 106 (2022) 1, 016002, arXiv: 2204.11519.

 

We investigate the dynamical spin polarization of a massless electron probing an electron plasma in locally thermal equilibrium via the Moller scattering from the quantum kinetic theory. We derive an axial kinetic equation delineating the dynamical spin evolution in the presence of the collision term with quantum corrections up to O(ℏ) and the leading-logarithmic order in coupling by using the hard-thermal-loop approximation, from which we extract the spin-polarization rate induced by the spacetime gradients of the medium. When the electron probe approaches local equilibrium, we further simplify the collision term into a relaxation-time expression. Our kinetic equation may be implemented in the future numerical simulations for dynamical spin polarization.

 

(6) Ren-jie Wang, Shuo Lin, Shi Pu, Yi-fei Zhang, Qun Wang, Lepton pair photoproduction in peripheral relativistic heavy-ion collisions, Phys. Rev. D 106 (2022) 3, 034025, arXiv:  2204.02761.

 

We study the lepton pair photoproduction in peripheral heavy-ion collisions based on the formalism in our previous work [R.-j. Wang, S. Pu, and Q. Wang, Phys. Rev. D 104, 056011 (2021)]. We present the numerical results for the distributions of the transverse momentum, azimuthal angle and invariant mass for e⁺ e^- and  μ⁺ μ^-  pairs as functions of the impact parameter and other kinematic variables in Au+Au collisions. Our calculation incorporates the information on the transverse momentum and polarization of photons which is essential to describe the experimental data. We observe a broadening effect in the transverse momentum for lepton pairs with and without smear effects. We also observe a significant enhancement in the distribution of cos(2φ) for μ⁺ μ^- pairs. Our results provide a baseline for future studies of other higher order corrections beyond Born approximation and medium effects in the lepton pair production.

 

(5) Xiang-Yu Wu, Cong Yi, Guang-You Qin, Shi Pu,  Local and global polarization of Λ hyperons across RHIC-BES energies: The roles of spin hall effect, initial condition, and baryon diffusion Phys. Rev. C 105 (2022) 6, 064909, arXiv: 2204.02218.

 

We perform a systematic study on the local and global spin polarization of Λ and Λ¯ hyperons in relativistic heavy-ion collisions at beam energy scan energies via the (3+1)-dimensional CLVisc hydrodynamics model with a multiphase transport (AMPT) and simulating many accelerated strongly interacting hadron (SMASH) initial conditions. Following the quantum kinetic theory, we decompose the polarization vector as the parts induced by thermal vorticity, shear tensor and the spin Hall effect (SHE). We find that the polarization induced by the SHE and the total polarization strongly depends on the initial conditions. At 7.7GeV, the SHE gives a sizable contribution and even flips the sign of the local polarization along the beam direction for the AMPT initial condition, which is not observed for the SMASH initial condition. Meanwhile, the local polarization along the out-of-plane direction induced by the SHE with the AMPT initial condition does not always increase with decreasing collision energies. Next, we find that the polarization along the beam direction is sensitive to the baryon diffusion coefficient, but the local polarization along the out-of-plane direction is not. Our results for the global polarization of Λ and Λ¯ agree well with the data of the STAR Collaboration. Interestingly, the global polarization of Λ¯ is not always larger than that of Λ due to various competing effects. Our findings are helpful for understanding the polarization phenomenon and the detailed structure of quark-gluon plasma in relativistic heavy-ion collisions.

(4) Patrick Copinger, Shi Pu, Berry phase in the phase space worldline representation: The axial anomaly and classical kinetic theory, Phys.Rev.D 105 (2022) 11, 116014, arXiv: 2203.00847

 

The Berry phase is analyzed for Weyl and Dirac fermions in a phase space representation of the worldline formalism. Kinetic theories are constructed for both at a classical level. Whereas the Weyl fermion case reduces in dimension, resembling a theory in quantum mechanics, the Dirac fermion case takes on a manifestly Lorentz covariant form. To achieve a classical kinetic theory for the non-Abelian Dirac fermion Berry phase a spinor construction of Barut and Zanghi is utilized. The axial anomaly is also studied at a quantum level. It is found that under an adiabatic approximation, which is necessary for facilitating a classical kinetic theory, the index of the Dirac operator for massless fermions vanishes. Even so, similarities of an axial rotation to an exact noncovariant Berry phase transform are drawn by application of the Fujikawa method to the Barut and Zanghi spinors on the worldline.

 

(3) Xin-Li Sheng, Yang Li, Shi Pu, Qun Wang, Lorentz Transformation in Maxwell Equations for Slowly Moving Media, Symmetry 14 (2022) 1641, arXiv: 2202.03122

 

We use the method of field decomposition, a widely used technique in relativistic magnetohydrodynamics, to study the small velocity approximation (SVA) of the Lorentz transformation in Maxwell equations for slowly moving media. The “deformed” Maxwell equations derived using SVA in the lab frame can be put into the conventional form of Maxwell equations in the medium’s co-moving frame. Our results show that the Lorentz transformation in the SVA of up to (v is the speed of the medium and c is the speed of light in a vacuum) is essential to derive these equations: the time and charge density must also change when transforming to a different frame, even in the SVA, not just the position and current density, as in the Galilean transformation. This marks the essential difference between the Lorentz transformation and the Galilean one. We show that the integral forms of Faraday and Ampere equations for slowly moving surfaces are consistent with Maxwell equations. We also present Faraday equation in the covariant integral form, in which the electromotive force can be defined as a Lorentz scalar that is independent of the observer’s frame. No evidence exists to support an extension or modification of Maxwell equations.

 

(2) Yoshimasa Hidaka, Shi Pu, Qun Wang, Foundations and applications of quantum kinetic theory, Prog. Part. Nucl. Phys. 127 (2022) 103989, arXiv: 2201.07644  (Invited Review)

 

Many novel quantum phenomena emerge in non-equilibrium relativistic quantum matter under extreme conditions such as strong magnetic fields and rotations. The quantum kinetic theory based on Wigner functions in quantum field theory provides a powerful and effective microscopic description of these quantum phenomena. In this article we review some of recent advances in the quantum kinetic theory and its applications in describing these quantum phenomena.

(1) Jun-Jie Zhang, Xin-Li Sheng, Shi Pu, Jian-Nan Chen, Guo-Liang Peng, Phys.Rev.Res. 4 (2022) 3, 033138, arXiv: 2201.06171

 

We have calculated the directed flow $v_{1}$ and charge-dependent directed flow $\Delta v_{1}$ for pions and protons in Au+Au collisions at $\sqrt{s_{NN}}=200$GeV by solving the coupled Boltzmann-Maxwell equations self-consistently. Our numerical results show that $v_{1}$ for pions and protons are all negative in the positive mid rapidity region and have similar behavior  and magnitude. In contrast we find a quite different behavior in $\Delta v_{1}$ for pions and protons. The difference lies in that $\Delta v_{1}$ for protons mainly comes from pressure gradients of the medium, while the dominant contribution to $\Delta v_{1}$ for pions is from electromagnetic fields. Our results indicate that the effect of the electric field will slightly exceed that of the magnetic and lead to a small negative slope of $\Delta v_{1}$ for pions.