Non-perturbative investigation of current correlators in twisted mass lattice QCD

We present an investigation of hadronic current-current correlators based on the first principles of Quantum Chromodynamics. Specifically we apply the non-perturbative methods of twisted mass lattice QCD with dynamical up and down quark taking advantage of its automatic O(a) improvement. As a special application we discuss the calculation of the hadronic leading order contribution to the muon anomalous magnetic moment. The latter is regarded as a promising quantity for the search for physics beyond the standard model. The origin of the strong interest in the muon anomaly lies in the persistent discrepancy between the standard model estimate and its experimental measurement. In the theoretical determination the hadronic leading order part is currently afflicted with the largest uncertainty and a dedicated lattice investigation of the former can be of strong impact on future estimates. We discuss our study of all systematic uncertainties in the lattice calculation, including three lattice volumes, two lattice spacings, pion masses from 650 MeV to 290 MeV and the quark-disconnected contribution. We present a new method for the extrapolation to the physical point that softens the pion mass dependence of aμhlo and allows for a linear extrapolation with small statistical uncertainty at the physical point. We determine the contribution of up and down quark as aμhlo(Nf=2)=5.69(15)10-8. The methods used for the muon are extended to the electron and tau lepton and we find aehlo(Nf=2)=1.512(43)10-12 and aτhlo(Nf=2)=2.635(54)10-6. We estimate the charm contribution to aμhlo in partially quenched tmLQCD with the result aμhlo(charm)=1.447(24)(30)10-9 in very good agreement with a dispersion-relation based result using experimental data for the hadronic R-ratio.