A.C. Irving

A Comprehensive lattice study of SU(3) glueballs

We present a study of the SU(3) glueball spectrum for all JPC values at lattice spacings down to a−1 = 3.73(6) GeV (β = 6.4) using lattices of size up to 324. We extend previous studies and show that the continuum limit has effectively been reached. The number of clearly identified JPC states has been substantially increased. There are no clear signals for spin-exotic glueballs below 3 GeV. A comparison with current experimental glueball candidates is made.

Effects of nonperturbatively improved dynamical fermions in QCD at fixed lattice spacing

We present results for the static inter-quark potential, lightest glueballs, light hadron spectrum and topological susceptibility using a non-perturbatively improved action on a

The nucleon mass in Nf=2 lattice QCD: Finite size effects from chiral perturbation theory

16^3\times 32

A determination of the Lambda parameter from full lattice QCD

lattice at a set of values of the bare gauge coupling and bare dynamical quark mass chosen to keep the lattice size fixed in physical units (

Determination of light and strange quark masses from two-flavour dynamical lattice QCD

\sim 1.7

Improved Wilson QCD simulations with light quark masses

fm). By comparing these measurements with a matched quenched ensemble, we study the effects due to two degenerate flavours of dynamical quarks. With the greater control over residual lattice spacing effects which these methods afford, we find some evidence of charge screening and some minor effects on the light hadron spectrum over the range of quark masses studied (

Glueball mass measurements from improved staggered fermion simulations

M_{PS}/M_{V}\ge0.58

Instability in the molecular dynamics step of a hybrid Monte Carlo algorithm in dynamical fermion lattice QCD simulations

). More substantial differences between quenched and unquenched simulations are observed in measurements of topological quantities.

Is the up-quark massless?

Abstract In the framework of relativistic SU(2) f baryon chiral perturbation theory we calculate the volume dependence of the nucleon mass up to and including O ( p 4 ). Since the parameters in the resulting finite size formulae are fixed from the pion mass dependence of the large volume nucleon masses and from phenomenology, we obtain a parameter-free prediction of the finite size effects. We present mass data from the recent N f =2 simulations of the UKQCD and QCDSF Collaborations and compare these data as well as published mass values from the dynamical simulations of the CP-PACS and JLQCD Collaborations with the theoretical expectations. Remarkable agreement between the lattice data and the predictions of chiral perturbation theory in a finite volume is found.

Mathematical Explorations with MATLAB

We present a determination of the QCD parameter Lambda in the quenched approximation (n_f=0) and for two flavours (n_f=2) of light dynamical quarks. The calculations are performed on the lattice using O(a) improved Wilson fermions and include taking the continuum limit. We find Lambda_{n_f=0} = 259(1)(20) MeV and Lambda_{n_f=2} = 261(17)(26) MeV}, using r_0 = 0.467 fm to set the scale. Extrapolating our results to five flavours, we obtain for the running coupling constant at the mass of the Z boson alpha_s(m_Z) = 0.112(1)(2). All numbers refer to the MSbar scheme.