Search

We compute the leading QED corrections to the hadronic vacuum polarization (HVP) of the photon, relevant for the determination of leptonic anomalous magnetic moments, al. We work in the electroquenched approximation and use dynamical QCD configurations generated by the CLS initiative with two degenerate flavors of nonperturbatively O(a)-improved Wilson fermions. We consider QEDL and QEDM to deal with the finite-volume zero modes. We compare results for the Wilson loops with exact analytical determinations. In addition we make sure that the volumes and photon masses used in QEDM are such that the correct dispersion relation is reproduced by the energy levels extracted from the charged pions two-point functions. Finally we compare results for pion masses and the HVP between QEDL and QEDM. For the vacuum polarization, corrections with respect to the pure QCD case, at fixed pion masses, turn out to be at the percent level.

We nonperturbatively determine the renormalization factor of the axial vector current in lattice QCD with Nf=3 flavors of Wilson-clover fermions and the tree-level Symanzik-improved gauge action. The (by now standard) renormalization condition is derived from the massive axial Ward identity, and it is imposed among Schrödinger functional states with large overlap on the lowest lying hadronic state in the pseudoscalar channel, in order to reduce kinematically enhanced cutoff effects. We explore a range of couplings relevant for simulations at lattice spacings of ≈0.09 fm and below. An interpolation formula for ZA(g02), smoothly connecting the nonperturbative values to the 1-loop expression, is provided together with our final results.

We present a study of the B spectrum performed in the framework of heavy quark effective theory expanded to next-to-leading order in 1/mb and nonperturbative in the strong coupling. Our analyses have been performed on Nf=2 lattice gauge field ensembles corresponding to three different lattice spacings and a wide range of pion masses. We obtain the Bs-meson mass and hyperfine splittings of the B- and Bs-mesons that are in good agreement with the experimental values and examine the mass difference mBs-mB as a further cross-check of our previous estimate of the b-quark mass. We also report on the mass splitting between the first excited state and the ground state in the B and Bs systems, We acknowledge partial support by the SFB/TR 9, by Grants No. HE 4517/2-1 (P. F. and J. H.) and No. HE 4517/3-1 (J. H.) of the Deutsche Forschungsgemeinschaft, by the European Community through EU Contract No. MRTN-CT-2006-035482, “FLAVIAnet,” by the Spanish Minister of Education and Science projects RyC-2011-08557 and by the Danish National Research Foundation under Grant No. DNRF:90 (M. D. M.). P. F. acknowledges financial support from the Spanish MINECO under Grants No. FPA2012-31880 and No. SEV-2012-0249 (“Centro de Excelencia Severo Ochoa” Programme). N. G. is supported by the Leverhulme trust, research Grant No. RPG-2014-118. We gratefully acknowledge the computer resources granted by the John von Neumann Institute for Computing (NIC) and provided on the supercomputer JUROPA at Jülich Supercomputing Centre (JSC) and by the Gauss Centre for Supercomputing (GCS) through the NIC on the GCS share of the supercomputer JUQUEEN at JSC, with funding by the German Federal Ministry of Education and Research (BMBF) and the German State Ministries for Research of Baden-Württemberg (MWK), Bayern (StMWFK) and Nordrhein-Westfalen (MIWF), as well as within the Distributed European Computing Initiative by the PRACE-2IP, with funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under Grant Agreement No. RI-283493, by the Grand Équipement National de Calcul Intensif at CINES in Montpellier under the allocation 2012-056808, by the HLRN in Berlin, and by NIC at DESY, Zeuthen

We present a study of the B spectrum performed in the framework of Heavy Quark Effective Theory expanded to next-to-leading order in 1/m and non-perturbative in the strong coupling. Our analyses have been performed on Nf=2 lattice gauge field ensembles corresponding to three different lattice spacings and a wide range of pion masses. We obtain the Bs-meson mass and hyperfine splittings of the B- and Bs-mesons that are in good agreement with the experimental values and examine the mass difference m_{Bs}-m_B as a further cross-check of our previous estimate of the b-quark mass. We also report on the mass splitting between the first excited state and the ground state in the B and Bs systems.

We report our final estimate of the b-quark mass from Nf=2 lattice QCD simulations using Heavy Quark Effective Theory non-perturbatively matched to QCD at O(1/mh). Treating systematic and statistical errors in a conservative manner, we obtain m¯bMS¯(2 GeV)=4.88(15) GeV after an extrapolation to the physical point.

We convey an idea of the significant recent progress, which opens up good perspectives for high-precision ab-initio computations in heavy flavour physics based on lattice QCD. Rather than surveying the latest results, this contribution focuses on the concept and the challenges of fully non-perturbative computations in the B-meson sector, where the b-quark is treated within an effective theory. We outline its use to determine the b-quark mass and report on the results obtained in the quenched approximation and on the status in the two dynamical flavour theory., Comment: Contribution to the NIC-Symposium 2010, 24-25 February 2010, Juelich, Germany; 8 pages including figures, latex2e, uses nic-series.cls

Using iso-spin symmetry the quark-connected and disconnected contributions to the hadronic vacuum polarisation in a theory with N_f=2 flavours can be described as independent correlation functions, respectively. We show how this allows to use twisted boundary conditions for the connected contribution in order to improve the q^2-resolution in lattice QCD. Furthermore we derive an exact relation between the connected and the disconnected contributions at NLO in chiral perturbation theory. We discuss extensions to theories with more than 2 dynamical flavours., Comment: 7 pages, 1 figure, 1 table, Talk presented at The XXVII International Symposium on Lattice Field Theory, LATTICE 2009 - Peking University, Beijing, China / July 26 - 31, 2009

A non perturbative method to compute the mass of the b quark including the 1/m term in HQET has been presented in a companion talk. Following this strategy, we find in the MS bar scheme m_b^{stat}(m_b) = 4.350(64) GeV for the leading term, and m_b^{(1)}(m_b) = -0.049(29) GeV for the next to leading order correction. This method involves several steps, including the simulation of the relativistic theory in a small volume, and of the effective theory in a big volume. Here we present some numerical details of our calculations., 7 pages, 5 figures, talk presented at Lattice 2005 (Heavy quark physics), PoS style. Add reference to hep-lat/0510048

We consider HQET including the first order correction in 1/m. A strategy for the computation of the b-quark mass is discussed. Only two quantities Phi_1/2 have to be considered in order to match QCD and HQET, since the spin-dependent interaction is easily eliminated due to the spin symmetry of the static theory. Quite simple formulae relate the renormalization group invariant b-quark mass (M_b) to the B-meson mass. All entries in these formulae are non-perturbatively defined and can be computed in the continuum limit of the lattice regularized theory. For the numerically most critical part, we illustrate the cancellation of power divergences by a numerical example. Numerical results for the 1/m correction to M_b, are presented in a companion talk., Talk presented at Lattice 2005 (Heavy quark physics), 5 pages

We explain how the strategy of solving renormalization problems in HQET non-perturbatively by a matching to QCD in finite volume can be implemented to include dynamical fermions. As a primary application, some elements of an HQET computation of the mass of the b-quark beyond the leading order with N_f=2 are outlined. In particular, the matching of HQET and QCD requires relativistic QCD simulations in a volume with L ~ 0.5 fm, which will serve to quantitatively determine the heavy quark mass dependence of heavy-light meson observables in the continuum limit of finite-volume two-flavour lattice QCD. As a preparation for the latter, we report on our determination of the renormalization constants and improvement coefficients relating the renormalized current and subtracted bare quark mass in the relevant weak coupling region. The calculation of these coefficients employs a constant physics condition in the Schroedinger functional scheme, where the box size L is fixed by working at a prescribed value of the renormalized coupling., Comment: 14 pages including figures and tables, latex2e, uses PoS.cls; presented at the XXV International Symposium on Lattice Field Theory, July 30 - August 4 2007, Regensburg, Germany; typo corrected, results unchanged