Feynman diagrams representing processes contributing to the muon's anomalous magnetic moment. 

     In each diagram, the bottom photon represents coupling to the external magnetic field B

     The first three are standard-model contributions: 

(a) A single virtual-photon loop gives the leading QED term. 

(b) Virtual hadron pairs contribute to vacuum polarization.

(c) A loop with virtual W bosons and a neutrino contributes to electroweak radiative corrections. 

(d) Beyond the standard model, a conjectural contribution involves a sneutrino () loop. 

The virtual chargino () is a superposition of the supersymmetric partners of the Higgs and W bosons. 
 © 2001 American Institute of Physics