arXiv subjects

Shi-Zheng Yang

Publications and source records attributed to Shi-Zheng Yang.

8 recordsLinked to original sources

arXiv2026

Weyl anomaly induced transport in hydrodynamics

We show that the Weyl (trace) anomaly gives rise to a new non-dissipative vector current in accelerated relativistic fluids. The anomaly uniquely fixes the second-order transport coefficient governing the coupling between the electromagnetic field and the fluid acceleration. We derive this result by extending hydrodynamic anomaly matching to include the trace anomaly, and independently reproduce it in boundary quantum field theory by treating the Rindler horizon of an accelerated observer as an effective boundary. From the boundary perspective, the electric- and magnetic-field sectors correspond to screening and vacuum magnetization effects near the boundary. In the local rest frame, the electric-field contribution induces an additional charge density, while the magnetic-field contribution generates a transverse current with a Nernst-like, more generally thermomagnetic Hall-like, tensor structure. Our results reveal a new class of anomaly-induced transport governed by the trace anomaly.

hep-th↗

arXiv2025

Second-order chiral kinetic theory from Wigner function approach

We present a systematic method to derive the chiral kinetic theory from the Wigner equations based on quantum field theory order by order. We take special effort to derive the chiral kinetic theory in seven-dimensional phase space from the eight-dimensional chiral kinetic theory. We give the seven-dimensional chiral kinetic theory up to second order of semiclassical expansion. We find some new second-order contributions compared with other approaches.

hep-ph↗

arXiv2024

Spin alignment of vector mesons in local equilibrium by Zubarev's approach

We compute the $00$ element of the spin density matrix, denoted as $ρ_{00}$ and called the spin alignment, up to the second order of the gradient expansion in local equilibrium by Zubarev's approach. In the first order, we obtain $ρ_{00}=1/3$, meaning that the contributions from thermal vorticity and shear stress tensor are vanishing. The non-vanishing contributions to $ρ_{00}-1/3$ appear in the second order of gradients in the Belinfante and canonical cases. We also discuss the properties of the spin density matrix under the time reversal transformation. The effective transport coefficient for the spin alignment induced by the thermal shear stress tensor is T-odd in the first order, implying that the first order effect is dissipative.

hep-ph↗

arXiv2024

Corrections from space-time dependent electromagnetic fields to Wigner functions and spin polarization

We have derived the Wigner equations at global equilibrium with constant vorticity but space-time dependent electromagnetic fields up to second order in semiclassical expansion. We obtain the new second-order contributions to the charge currents and energy-momentum tensor from the varying electromagnetic fields. We also compute the new corrections to the spin polarization pesudo-vector from both contant and varying electromagnetic fields. We also find that the space-time dependent electromagnetic field provides a tighter constraint on the solutions of Wigner functions in global equilibrium compared with constant electromagnetic field.

hep-ph↗

arXiv2024

Linear response theory for spin alignment of vector mesons in thermal media

We present a calculation of the spin alignment for unflavored vector mesons in thermalized quark-gluon plasma based on the Kubo formula in linear response theory. This is achieved by expanding the system to the first order of the coupling constant and the spatial gradient. The effect strongly relies on the vector meson's spectral functions which are determined by the interaction and medium properties. The spectral functions are calculated for the one-quark-loop self-energy with meson-quark interaction. The numerical results show that the correction to the spin alignment from the thermal shear tensor is of the order $10^{-4}\sim10^{-5}$ for the chosen values of quark-meson coupling constant, if the magnitude of thermal shear tensor is $10^{-2}$.

hep-ph↗

arXiv2023

Revisit spin effects induced by thermal vorticity

We revisit the spin effects induced by thermal vorticity by calculating them directly from the spin-dependent distribution functions. For the spin-1/2 particles, we give the polarization up to the first order of thermal vorticity and compare it with the usual result calculated from the spin vector. For the spin-1 particles, we find that all the non-diagonal elements vanish and there is no spin alignment up the first order of thermal vortcity. We present the spin alignment at second-order contribution from thermal vorticity. We also find that the spin effects for both Dirac and vector particles will receive extra contribution when the spin direction is associated with the particle's momentum.

hep-ph↗

arXiv2022

Constraining non-dissipative transport coefficients in global equilibrium

The fluid in global equilibrium must fulfill some constraints. These constraints can be derived from quantum statistical theory or kinetic theory. In this paper we will show that how these constraints can be applied to determine the non-dissipative transport coefficients for chiral systems along with the energy-momentum conservation, chiral anomaly for charge current and trace anomaly in energy-momentum tensor.

hep-ph↗

arXiv2020

Second-order Charge Currents and Stress Tensor in Chiral System

We solve the Wigner equation for massless spin-1/2 charged fermions near global equilibrium. The Wigner function can be obtained order by order in the power expansion of the vorticity and electromagnetic field. The Wigner function has been derived up to the second order from which the non-dissipative charge currents and the stress tensor can be obtained. The charge and energy densities and the pressure have contributions from the vorticity and electromagnetic field at the second order. The vector and axial Hall currents can be induced along the direction orthogonal to the vorticity and electromagnetic field at the second order. We also find that the trace anomaly emerges natually in renormalizing the stress tensor by including the quantum correction from the electromagnetic field.

hep-ph↗