Here u ( p i ) and u ¯ ¯ ( p f ) are 4-spinor solutions of the Dirac equation normalized so that u ¯ ¯ u = 2 m e , and q μ μ = p f μ μ − − p i μ μ is the momentum transfer from the current to the electron. The q 2 = 0 form factor F 1 ( 0 ) = Q is the electron's charge, μ μ = F 1 ( 0 ) + F 2 ( 0 ) 2 m e is its static magnetic dipole moment, and − − F 3 ( 0 ) 2 m e provides the formal definition of the electron's electric dipole moment. The remaining form factor F 4 ( q 2 ) would, if nonzero, be the anapole moment.