Perturbative renormalisation of quark bilinear operators for overlap fermions with and without stout links and improved gauge action

We calculate lattice renormalisation constants of local and one-link quark operators for overlap fermions and improved gauge actions in one-loop perturbation theory. For the local operators we stout smear the SU(3) links in the fermionic action. Using the popular tadpole improved L\"uscher-Weisz actions at $\beta=8.45$ and $\beta=8.0$ we present numerical values for the Z factors in the $\bar{MS}$ scheme (partly as function of the stout smearing strength). We compare various levels of mean field (tadpole) improvement which have been applied to our results.Comment: 7 page

One-loop renormalisation of quark bilinears for overlap fermions with improved gauge actions

We compute lattice renormalisation constants of local bilinear quark operators for overlap fermions and improved gauge actions. Among the actions we consider are the Symanzik, L\"uscher-Weisz, Iwasaki and DBW2 gauge actions. The results are given for a variety of $\rho$ parameters. We show how to apply mean field (tadpole) improvement to overlap fermions. The question, what is a good gauge action, is discussed from the perturbative point of view. Finally, we show analytically that the gauge dependent part of the self-energy and the amputated Green functions are independent of the lattice fermion representation, using either Wilson or overlap fermions.Comment: 38 pages, 5 figures, v2: Numbers in Tables 1-4,7-10 corrected, Figs. 4,5 updated, 2 misprints in (A.2), (A.4) correcte

Non-perturbative renormalisation for overlap fermions

Using non-perturbative techniques we have found the renormalisation factor, Z, in the RI-MOM scheme for quark bilinear operators in quenched QCD. We worked with overlap fermions using the Luescher-Weisz gauge action. Our calculation was performed at beta=8.45 at a lattice spacing of 1/a=2.1 GeV using a value of rho=1.4. Our results show good agreement between the vector and the axial vector in the zero mass limit. This shows that overlap fermions have good chiral properties. To attempt to improve the discretisation errors in our results we subtracted the O(a^2) terms in one-loop lattice perturbation theory from the Monte Carlo Green functions. In particular we paid attention to the operators for the observable . We found a value for the renormalisation constants Z^msbar_(v_2b) and Z^msbar_(v_2a) just less than 1.9 at mu=1/a=2.1 GeV.Comment: 6 pages, 3 figures, uses PoS style, poster presented at Lattice 2005 (Chiral Fermions), to be published in Proceedings of Scienc

Strange quark mass from Finite Energy QCD sum rules to five loops

The strange quark mass is determined from a new QCD Finite Energy Sum Rule (FESR) optimized to reduce considerably the systematic uncertainties arising from the hadronic resonance sector. As a result, the main uncertainty in this determination is due to the value of $\Lambda_{QCD}$. The correlator of axial-vector divergences is used in perturbative QCD to five-loop order, including quark and gluon condensate contributions, in the framework of both Fixed Order (FOPT), and Contour Improved Perturbation Theory (CIPT). The latter exhibits very good convergence, leading to a remarkably stable result in the very wide range $s_0 = 1.0 - 4.0 {GeV}^2$, where $s_0$ is the radius of the integration contour in the complex energy (squared) plane. The value of the strange quark mass in this framework at a scale of 2 GeV is $m_s(2 {GeV}) = 95 \pm 5 (111 \pm 6) {MeV}$ for $\Lambda_{QCD} = 420 (330) {MeV}$, respectively.Comment: Additional comments added at the end of the Conclusions, and one extra reference is given. A note added in proof uses the most recent determination of Lambda_QCD from ALEPH to narrow down the predictio

Three-particle contributions to the renormalisation of B-meson light-cone distribution amplitudes

We study light-cone distribution amplitudes of heavy-light systems, such as a B-meson. By an explicit computation, we determine how two-parton distribution amplitudes mix with three-parton ones at one loop: \phi_+ is shown to mix only into itself, whereas \phi_- mixes with the difference of three-parton distribution amplitudes \Psi_A-\Psi_V. We determine the corresponding anomalous dimension and we check the gauge independence of our result by considering a general covariant gauge. Finally, we comment on some implications of our result for phenomenological models of these distribution amplitudes.Comment: 21 pages, 5 figures, some comments and 2 references added, except for typesetting matches version published in JHE

International Lattice Data Grid

We propose the co-ordination of lattice QCD grid developments in different countries to allow transparent exchange of gauge configurations in future, should participants wish to do so. We describe briefly UKQCD's XML schema for labelling and cataloguing the data. A meeting to further develop these ideas will be held in Edinburgh on 19/20 December 2002, and will be available over AccessGrid.Comment: Lattice2002(plenary

QCD with light Wilson quarks on fine lattices (II): DD-HMC simulations and data analysis

In this second report on our recent numerical simulations of two-flavour QCD, we provide further technical details on the simulations and describe the methods we used to extract the meson masses and decay constants from the generated ensembles of gauge fields. Among the topics covered are the choice of the DD-HMC parameters, the issue of stability, autocorrelations and the statistical error analysis. Extensive data tables are included as well as a short discussion of the quark-mass dependence in partially quenched QCD, supplementing the physics analysis that was presented in the first paper in this series.Comment: TeX source, 35 pages, figures include

Accelerating Hasenbusch's acceleration of Hybrid Monte Carlo

Hasenbusch has proposed splitting the pseudo-fermionic action into two parts, in order to speed-up Hybrid Monte Carlo simulations of QCD. We have tested a different splitting, also using clover-improved Wilson fermions. An additional speed-up between 5 and 20% over the original proposal was achieved in production runs.Comment: Poster presented by H. Stueben at Lattice2003, meta-data correcte