The Anomaly in the Electron Orbital g-factor and the Search for New Physics

High precision measurements of the electron spin and/or orbital g-factor complement very well, the atomic/molecular experiments which test for parity, search for a permanent electric dipole moment and test the CPT Theorem, or investigate the Lorentz symmetry and test QED. A search for an anomaly in the electron g-factors also provides a stringent test of QED (and therefore the Standard Model), in which it is currently assumed that the orbital g-factor is unaffected by the radiative interactions, though the anomaly (g_S – 2) in the spin g-factor is attributed to radiative corrections. Furthermore, it is currently assumed, without the benefit of sufficient experimental investigations, that the electron has a uniform mass-to-charge distribution like a classical point particle, hence its orbital g-factor must be exactly equal to one, i.e, g_L = 1. Nevertheless, determinations from the measurement of the ratio of g_J values in In, Ga, Na, Ar, Ne and He, indicate that the anomaly in the electron orbital g-factor is of the order of 10^-3 to 10^-4 to very high precisions. Therefore, continued search for anomalies  in the electron spin and orbital g-factors, or, alternatively high-precision measurements of the electron factors, will constitute a useful guide in the search for new physics beyond the Standard Model, while also providing a low-energy means of elucidating the nature or structure of the electron.