The leading disconnected contribution to the anomalous magnetic moment   of the muon
  The hadronic vacuum polarization can be determined from the vector correlator in a mixed time-momentum representation. We explicitly calculate the disconnected contribution to the vector correlator, both in the $N_f = 2$ theory and with an additional quenched strange quark, using non-perturbatively $O(a)$-improved Wilson fermions. All-to-all propagators are computed using stochastic sources and a generalized hopping parameter expansion. Combining the result with the dominant connected contribution, we are able to estimate an upper bound for the systematic error that arises from neglecting the disconnected contribution in the determination of $(g-2)_\mu$. 
Anthony Francis, Vera G\"ulpers, Benjamin J\"ager, Harvey Meyer, Georg   von Hippel, Hartmut Wittig
hep-lat