Chiral anomaly and the law of conservation of momentum in 3He-A
Volovik G. E.
The nonconservation of momentum of the fermion vacuum in superfluid 3He-A at Τ = 0 is the result of chiral anomaly which is completely analogous to the axial-current anomaly in quantum chromodynamics. The effective "electromagnetic" fields, whose role in 3He-A is played by the order-parameter gradients, produce a momentum source of the form F*v F μν. This Schwinger source describes the transfer of momentum between the fermion vacuum and the excitation system.