From Kadanoff-Baym to Boltzmann equations for massive spin-1/2 fermions

We derive Boltzmann equations for massive spin- fermions with local and nonlocal collision terms from the Kadanoff-Baym equation in the Schwinger-Keldysh formalism, properly accounting for the spin degrees of freedom. The Boltzmann equations are expressed in terms of matrix-valued spin distribution functions, which are the building blocks for the quasiclassical parts of the Wigner functions. Nonlocal collision terms appear at next-to-leading order in and are sources for the polarization part of the matrix-valued spin distribution functions. The Boltzmann equations for the matrix-valued spin distribution functions pave the way for simulating spin-transport processes involving spin-vorticity couplings from first principles.