The axial current resulting from the motion of an axially charged moving particle is formally defined as j 5 μ μ = ψ ψ ¯ ¯ γ γ 5 γ γ μ μ ψ ψ , where ψ ψ is the particle field represented by Dirac spinor (since the particle is typically a spin -1/2 fermion) and γ γ 5 and γ γ μ μ are the Dirac gamma matrices.