Testing new physics with the electron g-2

We argue that the anomalous magnetic moment of the electron (a(e)) can be used to probe new physics. We show that the present bound on new-physics contributions to a(e) is 8 x 10(-13), but the sensitivity can be improved by about an order of magnitude with new measurements of a(e) and more refined determinations of alpha in atomic-physics experiments. Tests on new-physics effects in a(e) can play a crucial role in the interpretation of the observed discrepancy in the anomalous magnetic moment of the muon (a(mu)). In a large class of models, new contributions to magnetic moments scale with the square of lepton masses and thus the anomaly in a(mu) suggests a new-physics effect in a(e) of (0.7 +/- 0.2) x 10(-13). We also present examples of new-physics theories in which this scaling is violated and larger effects in a(e) are expected. In such models the value of a(e) is correlated with specific predictions for processes with violation of lepton number or lepton universality, and with the electric dipole moment of the electron.