Nucleon Resonances from FLIC Fermions

Abstract

The Fat Link Irrelevant Clover (FLIC) fermion action and its associated phenomenology are described. The scaling analysis indicates FLIC fermions provide a new form of nonperturbative O(a) improvement where near-continuum results are obtained at finite lattice spacing. Spin- 1 and spin- 3 , even and odd parity nucleon resonances are investigated. §1. FLIC fermions The CSSM lattice collaboration has been examining the merits of a new lattice fermion action 1) in which the (irrelevant) operators introduced to remove fermion doublers and lattice spacing artifacts are constructed with smoothed (APE smeared 2) ) links. The use of links in which short-distance fluctuations have been removed simplifies the determination of the coefficients of the improvement terms. 3) Perturbative renormalizations are small for smeared links and tree-level estimates, or the mean-field improved estimates used here, are sufficient to remove O(a) errors in the lattice spacing a. The key is that both the energy dimension-five Wilson term and the Clover term 4) are constructed with smooth links, while the relevant operators, surviving in the continuum limit, are constructed with the original untouched links generated via standard Monte Carlo techniques. A key feature of FLIC fermions is that the construction of irrelevant operators using smoothed links facilitates the use of highly improved definitions of the QCD field strength tensor Fµν leaving errors of O(a 6 ). 5) We call this action the Fat-Link-Irrelevant-Clover (FLIC) fermion action. Figure 1 displays our most comprehensive scaling analysis to date. The FLIC action performs systematically better than the mean-field improved clover and competes well with those obtained with the NP-improved clover fermion action. 7) There are two different volumes used at a 2 σ ∼ 0.075. These reveal a finite volume effect, which increases the mass for the smaller volumes at a 2 σ ∼ 0.075 and ∼ 0.045. Examination of points from the small and large volumes separately indicates continued scaling toward the continuum limit. Focusing on simulation results from physical volumes with extents ∼ 2 fm and larger, we perform a simultaneous fit of the FLIC, NP-improved clover and Wilson fermion action results. The fits are constrained to have a common continuum limit and assume errors are O(a 2 ) for FLIC and NP-improved clover actions and O(a) for the Wilson action. These results indicate that FLIC fermions provide a new form of