Spin polarization and spin alignment from quantum kinetic theory with self-energy corrections

TL;DR

This paper develops a quantum kinetic theory for massive fermions incorporating self-energy corrections, revealing how these corrections influence spin polarization phenomena in relativistic heavy ion collisions.

Contribution

It introduces a formalism that includes self-energy effects into quantum kinetic equations, extending previous models and providing new insights into spin polarization mechanisms.

Findings

Self-energy gradients significantly affect spin polarization spectra.

Self-energy effects can dominate over collisional effects in certain regimes.

Modifications to spin alignment of mesons are predicted beyond local thermal equilibrium.

Abstract

We derive the quantum kinetic theory for massive fermions with collision terms and self-energy corrections based on quantum field theory. We adopt an effective power counting scheme with $\hbar$ expansion to obtain the leading-order perturbative solutions of the vector and axial Wigner functions and the corresponding kinetic equations. We observe that both the onshell relation and the structure of Wigner functions, along with the kinetic equations, are modified due to the presence of self-energies and their space-time gradients. We further apply our formalism to investigate the spin polarization phenomena in relativistic heavy ion collisions and derive the modification to the spin polarization spectrum of massive quarks. We find that the gradient of vector self-energy plays a similar role to the background electromagnetic fields, which induces a more dominant contribution than the collisional effects by a naive power counting in the gradient expansion and weak coupling. Our findings could further modify the spin polarization of strange quarks and spin alignment of $\phi$ mesons beyond local thermal equilibrium.