  The dynamical evolution of spin of a massive probe fermion in a massless hot
QED plasma at local equilibrium is investigated through the quantum kinetic
theory. We consider the massive probe fermion undergoing 2-by-2 Coulomb
scattering with the massless fermions in the medium. The axial kinetic equation
is derived including the collision terms to the first order of gradients and
leading logarithmic order of the coupling. The collision terms are vanishing at
global equilibrium, around which the relaxation time can be extracted as an
operator. We further decompose the axial kinetic equation into kinetic
equations of axial-charge density as well as the transverse magnetic dipole
moment, and illustrate the diffusion and polarization effect through
preliminary numerical analysis.
