Kinetic equations for massive Dirac fermions in electromagnetic field with non-Abelian Berry phase

Abstract

We derive a semi-classical effective action and the kinetic equation for massive Dirac fermions in electromagnetic fields. The non-Abelian Berry phase structure emerges from two helicity states of massive fermions with positive energy. The classical spin emerges as a vector in SU(2) helicity space. The continuity equations for the fermion number and the classical spin are derived. The fermion number is conserved while the spin charge is not conserved by anomaly. Previous results about the coefficients of the chiral magnetic effect for the fermion and axial currents in the chiral limit can be reproduced after including the anti-fermion contributions. This provides an example for the emerging spin and non-Abelian Berry phase of Dirac fermions arising from the fermion mass.