Relativistic spin transport theory for spin-1/2 fermions

Global polarization effect is an important physical phenomenon reflecting spin-orbit couplings in heavy ion collisions. Since STAR's observation of the global polarization of A hyperons in Au+Au collisions in 2017, this effect has attracted a lot of interests in the field. In the hot and dense matter produced in heavy ion collisions, the spin-orbit couplings come from non-local collisions between particles, in which the orbital angular momentum involves the space and momentum information of the colliding particles, so it is necessary to describe the particle collisions with spin-orbit couplings in phase space. In addition, the spin-orbit coupling is a quantum effect, which requires quantum theory. In combination of two aspects, the quantum kinetic theory based on covariant Wigner functions has become a powerful tool to describe the global polarization effect. In this paper, we introduce the quantum kinetic theory for spin-1/2 Fermion system based on Wigner functions as well as the spin transport theory developed on this basis. The recent research progress of spin transport theory provides a solid theoretical foundation for simulating the space-time evolution of spin polarization effects in heavy ion collisions.