J. N. Hedditch

Excited Baryons in Lattice QCD

We present first results for the masses of positive and negative parity excited baryons calculated in lattice QCD using an O(a^2)-improved gluon action and a fat-link irrelevant clover (FLIC) fermion action in which only the irrelevant operators are constructed with APE-smeared links. The results are in agreement with earlier calculations of N^* resonances using improved actions and exhibit a clear mass splitting between the nucleon and its chiral partner. An correlation matrix analysis reveals two low-lying J^P=(1/2)^- states with a small mass splitting. The study of different Lambda interpolating fields suggests a similar splitting between the lowest two Lambda1/2^- octet states. However, the empirical mass suppression of the Lambda^*(1405) is not evident in these quenched QCD simulations, suggesting a potentially important role for the meson cloud of the Lambda^*(1405) and/or a need for more exotic interpolating fields.

Pseudoscalar and vector meson form factors from lattice QCD

J. N. Hedditch, W. Kamleh, B. G. Lasscock, D. B. Leinweber, A. G. Williams, and J. M. Zanotti

Search for the pentaquark resonance signature in lattice QCD

Claims concerning the possible discovery of the {theta}{sup +} pentaquark, with minimal quark content uudds, have motivated our comprehensive study into possible pentaquark states using lattice QCD. We review various spin-(1/2) pentaquark interpolating fields in the literature and create a new candidate ideal for lattice QCD simulations. Using these interpolating fields we attempt to isolate a signal for a five-quark resonance. Calculations are performed using improved actions on a large 20{sup 3}x40 lattice in the quenched approximation. The standard lattice resonance signal of binding at quark masses near the physical regime, observed for established baryon resonances, is not observed for spin-(1/2) pentaquark states. Thus we find no evidence supporting the existence of a spin-(1/2) pentaquark resonance in quenched QCD.

Even parity excitations of the nucleon in lattice QCD

We study the spectrum of the even-parity excitations of the nucleon in quenched lattice QCD. We extend our earlier analysis by including an expanded basis of nucleon interpolating fields, increasing the physical size of the lattice, including more configurations to enhance statistics and probing closer to the chiral limit. With a review of world lattice data, we conclude that there is little evidence of the Roper resonance in quenched lattice QCD.

FLIC fermions and hadron phenomenology

Abstract.A pedagogical overview of the formulation of the Fat-Link-Irrelevant-Clover (FLIC) fermion action and its associated phenomenology is described. The scaling analysis indicates FLIC fermions provide a new form of nonperturbative

Low-lying eigenmodes of the Wilson–Dirac operator and correlations with topological objects

{\mathcal O}(a)

Hybrid meson spectrum from the FLIC action

improvement where near-continuum results are obtained at finite lattice spacing. Spin-(1/2) and spin-(3/2), even- and odd-parity baryon resonances are investigated in quenched QCD, where the nature of the Roper resonance and

Excited baryons from the FLIC fermion action

\Lambda^*(1405)

Light quark electromagnetic structure of baryons

are of particular interest. FLIC fermions allow efficient access to the light-quark-mass regime, where evidence of chiral nonanalytic behavior in the

1-+ exotic on the lattice with FLIC fermions

\Delta