Michele Della Morte

On the generalized eigenvalue method for energies and matrix elements in lattice field theory

We discuss the generalized eigenvalue problem for computing energies and matrix elements in lattice gauge theory, including effective theories such as HQET. It is analyzed how the extracted effective energies and matrix elements converge when the time separations are made large. This suggests a particularly efficient application of the method for which we can prove that corrections vanish asymptotically as exp(−(EN+1 − En) t). The gap EN+1 − En can be made large by increasing the number N of interpolating fields in the correlation matrix. We also show how excited state matrix elements can be extracted such that contaminations from all other states disappear exponentially in time. As a demonstration we present numerical results for the extraction of ground state and excited B-meson masses and decay constants in static approximation and to order 1/mb in HQET.

On lattice actions for static quarks

We introduce new discretizations of the action for static quarks. They achieve an exponential improvement (compared to the Eichten-Hill regularization) on the signal to noise ratio in static-light correlation functions. This is explicitly checked in a quenched simulation and it is understood quantitatively in terms of the self energy of a static quark and the lattice heavy quark potential at zero distance. We perform a set of scaling tests in the Schroedinger functional and find scaling violations in the O(a) improved theory to be rather small -- for one observable significantly smaller than with the Eichten-Hill regularization. In addition we compute the improvement coefficients of the static light axial current up to O(g_0^4) corrections and the corresponding renormalization constants non-perturbatively. The regularization dependent part of the renormalization of the b-quark mass in static approximation is also determined.

Non-perturbative quark mass renormalization in two-flavor QCD

Abstract The running of renormalized quark masses is computed in lattice QCD with two flavors of massless O ( a ) improved Wilson quarks. The regularization and flavor independent factor that relates running quark masses to the renormalization group invariant ones is evaluated in the Schrodinger functional scheme. Using existing data for the scale r 0 and the pseudoscalar meson masses, we define a reference quark mass in QCD with two degenerate quark flavors. We then compute the renormalization group invariant reference quark mass at three different lattice spacings. Our estimate for the continuum value is converted to the strange quark mass with the help of chiral perturbation theory.

Towards a precise lattice determination of the leading hadronic contribution to (g-2)_mu

A bstractWe report on our computation of the leading hadronic contribution to the anomalous magnetic moment of the muon using two dynamical flavours of non-perturbatively O(a) improved Wilson fermions. The strange quark is introduced in the quenched approximation. Partially twisted boundary conditions are applied to improve the momentum resolution in the relevant integral. Our results, obtained at three different values of the lattice spacing, allow for a preliminary study of discretization effects. We explore a wide range of lattice volumes, namely 2xa0fmu2009≤u2009Lu2009≤u20093xa0fm, with pion masses from 600 to 280xa0MeV and discuss different chiral extrapolations to the physical point. We observe a non-trivial dependence of

Non-perturbative improvement of the axial current for dynamical Wilson fermions

a_mu^{HLO}

Heavy quark effective theory computation of the mass of the bottom quark

on mπ especially for small pion masses. The final result,

Non-perturbative renormalization of the axial current with dynamical Wilson fermions

a_mu^{HLO} = 618left( {64} right) times {10^{ - 10}}

Quark disconnected diagrams in chiral perturbation theory

, is obtained by considering only the quark connected contribution to the vacuum polarization. We present a detailed analysis of systematic errors and discuss how they can be reduced in future simulations.

HQET at order 1/m: II. Spectroscopy in the quenched approximation

A non-perturbative determination of the axial current improvement coefficient cA is performed with two flavors of dynamical improved Wilson fermions and plaquette gauge action. The improvement condition is formulated with Schrodinger functional boundary conditions and enforced at constant physical volume. Large sensitivity is obtained by using two different pseudo-scalar states in the PCAC relation. We estimate the resulting correction to FPS at β = 5.2 to be around 10%.

Exploring the HMC trajectory-length dependence of autocorrelation times in lattice QCD

We present a fully non-perturbative computation of the mass of the b-quark in the quenched approximation. Our strategy starts from the matching of HQET to QCD in a finite volume and finally relates the quark mass to the spin averaged mass of the Bs meson in HQET. All steps include the terms of order Λ2/mb. Expanding on [1], we discuss the computation and renormalization of correlation functions at order 1/mb. With the strange quark mass fixed from the Kaon mass and the QCD scale set through r0 = 0.5xa0fm, we obtain a renormalization group invariant mass Mb = 6.758(86)xa0GeV or b(b) = 4.347(48)GeV in the scheme. The uncertainty in the computed Λ2/mb terms contributes little to the total error and Λ3/mb2 terms are negligible. The strategy is promising for full QCD as well as for other B-physics observables.