Testing new physics with the electron g − 2

Abstract

Abstract 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 × 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 α 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 μ ). In a large class of models, new contributions to magnetic moments scale with the square of lepton masses and thus the anomaly in a μ suggests a new-physics effect in a e of (0.7 ± 0.2) × 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.