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Yi-Liang Yin

Publications and source records attributed to Yi-Liang Yin.

6 recordsLinked to original sources
arXiv2026

Vector-Meson Spin Alignment from Anisotropic Quark or Hadron Coalescence

The distribution of particles is highly anisotropic in the initial stage of a heavy-ion collision. In this paper we demonstrate that this anisotropy induces a sizable effect on the spin alignment of vector mesons. We study two different production mechanisms for $ϕ$ and $K^{*0}$ mesons, on one hand the coalescence of quarks and on the other that of pseudoscalar mesons. In the quark-coalescence picture where $ϕ$ and $K^{*0}$ are produced via a bare vector coupling to quarks, a negative $δρ_{00}^y$ of order $10^{-3}$ is observed. In contrast, when $ϕ$ and $K^{*0}$ are produced via quark coalescence with a vertex with spin-orbit coupling, or when they are produced via pseudoscalar-meson coalescence, a positive $δρ_{00}^y$ emerges. In all cases, the magnitude of the spin alignment is directly proportional to the degree of anisotropy. The sign difference between the cases provides a possibility to clarify the production mechanism for vector mesons.

hep-ph↗
arXiv2025

Spin density matrix for neutral $ρ$ mesons in a pion gas in linear response theory

We calculate the spin density matrix for neutral $ρ$ mesons from the spectral function and thermal shear tensor by Kubo formula in the linear response theory, which contributes to the $γ$ correlator for the CME search. We derive the spectral function of neutral $ρ$ mesons with $ρππ$ and $ρρππ$ interactions using the Dyson-Schwinger equation. The thermal shear tensor contribution is obtained from the Kubo formula in the linear response theory. We numerically calculate $ρ_{00}-1/3$ and $\mathrm{Re}ρ_{-1,1}$ using the simulation results for the thermal shear tensor by the hydrodynamical model, which are of the order $10^{-3}\sim10^{-2}$.

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↗
arXiv2024

The spin alignment of rho mesons in a pion gas

We study the spin alignment of neutral rho mesons in a pion gas using spin kinetic or Boltzmann equations. The $ρππ$ coupling is given by the chiral effective theory. The collision terms at the leading and next-to-leading order in spin Boltzmann equations are derived. The evolution of the spin density matrix of the neutral rho meson is simulated with different initial conditions. The numerical results show that the interaction of pions and neutral rho mesons creates very small spin alignment in the central rapidity region if there is no rho meson in the system at the initial time. Such a small spin alignment in the central rapidity region will decay rapidly toward zero in later time. If there are rho mesons with a sizable spin alignment at the initial time the spin alignment will also decrease rapidly. We also considered the effect on $ρ_{00}$ from the elliptic flow of pions in the blast wave model. With vanishing spin alignment at the initial time, the deviation of $ρ_{00}$ from 1/3 is positive but very small.

nucl-th↗
arXiv2022

Spin Boltzmann equation for non-relativistic spin-1/2 fermions

We derive the spin Boltzmann equations for spin-1/2 fermions in a non-relativistic model with four-fermion contact interaction which conserves spin degrees of freedom. A great advantage of the model is that the spin matrix elements in collision terms can be completely worked out and be put into such a compact form that one can clearly see how spins are coupled in particle scatterings. A semi-classical expansion in the Planck constant has been made and the on-shell part of the spin Boltzmann equation up to the next-to-leading order is derived. At the leading order the equilibrium spin distribution can be obtained from the vanishing of the collision term for the spin density. The spin chemical potential emerges as a natural consequence of spin conservation. The off-shell part of the spin Boltzmann equation is also discussed. The work can be extended to more sophisticated interaction such as nuclear force in order to apply to spin polarization phenomena in heavy-ion collisions at low energies.

nucl-th↗