Muon anomalous magnetic moment: A harbinger for “new physics”

Abstract

Standard model loop contributions to the muon anomalous magnetic moment, ${a}_{\ensuremath{\mu}}\ensuremath{\equiv}{(g}_{\ensuremath{\mu}}\ensuremath{-}2)/2,$ and their theoretical uncertainties are scrutinized. The status and implications of the recently reported 2.6 sigma experiment versus theory deviation ${a}_{\ensuremath{\mu}}^{\mathrm{expt}}\ensuremath{-}{a}_{\ensuremath{\mu}}^{\mathrm{SM}}=426(165)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}$ are discussed. Possible explanations due to supersymmetric loop effects with ${m}_{\mathrm{SUSY}}\ensuremath{\simeq}{55}_{\ensuremath{-}8}^{+16}\sqrt{\mathrm{tan}\ensuremath{\beta}} \mathrm{GeV},$ radiative mass mechanisms at the 1--2 TeV scale and other ``new physics'' scenarios are examined.