Charged Lepton G-2 and Constraints on New Physics

Abstract

A review of the theoretical and experimental values for the charged lepton (electron and muon) anomalous magnetic moment $a_l=(g_l-2)/2$ is presented. Employing the most accurate value for the fine structure constant ${\alpha }^{-1}=137.03599993(52)(0.0038ppm)$ obtained \cite {Kin196} from the electron $(g-2)$ we find the new complete standard model prediction for the anomalous magnetic moment of the muon $a_{\mu }^{th}=116591595(67)\times 10^{-11}$. The comparison of this theoretical value and the precise experimental result \cite {Sch} yields the estimation for the difference $\Delta a_{\mu }=a_{\mu }^{exp}-a_{\mu }^{th}$ at the 95% confidence level: $-95\times 10^{-10}\le \Delta a_{\mu }\le 236\times 10^{-10}$. The implication of the expected a factor of about 20 increase of accuracy in the forthcoming Brookhaven National Laboratory measurement of $a_{\mu }$ implies $-47\times 10^{-11}\le \Delta a_{\mu }\le 118\times 10^{-11}$, ($95$). This interval is used to get constraints on the "new physics". The value of the one-loop contributions $a_l^{B_i}$ of different bosons predicted within extension of the standard model and coupled to a charged lepton are discussed. The dependence of $a_l^{B_i}$ on the masses of the bosons and leptons of the vacuum polarization loops are investigated. The constraints on "new physics" by requiring that the new contributions $a_{\mu }^{B_i}$ to the muon anomalous magnetic moment lie within the latter interval $\Delta a_{\mu }$ are obtained.

22 pages, 5 figures, Talk given on the les Pecontres de Physique de la Vallee D'Aoste (Results and Perspectives in Particle Physics), 2-7 March,1998, La Thuile, Italy