Roberto Dale (Operations Research Center, University Miguel Hernández of Elche), Alicia Herrero and Juan Antonio Morales-Lladosa


For a single fermionic field, an interpretation of the Fierz identities (which establish relations between the bilinear field observables) is given. They appear closely related to the algebraic class (regular or singular) of the spin 2-form S associated to the spinor field. If S ≠ 0, the Fierz identities follow from the 3 + 1 decomposition of the eigenvector equations for S with respect to an inertial laboratory, which makes this interpretation suitable for fermionic particle physics models. When S = 0, the Fierz identities reduce to three constraints on the current densities associated with the spinor field, saying that they are orthogonal, equimodular, the vector current being time-like and the axial one being space-like.