http://hdl.handle.net/2440/10826 Fri, 24 May 2013 16:03:26 GMT 2013-05-24T16:03:26Z http://hdl.handle.net/2440/77618 Title: Resonant phase shift from finite volume interactions Author: Hsu, Anthony Chi-Pin; Hall, Jonathan Michael MacGillivray; Young, Ross Daniel; Thomas, Anthony William Abstract: A scattering process can be modelled by a finite volume lattice with appropriate boundary conditions. Such lattices have intermediate states with discretized energy spectrum. With Lüscher’s formula we can obtain the phase shifts of these states. We constructed a three dimensional, non-relativistic model for the scattering of two scalar mesons on a lattice. The resonant energy spectra at different lattice sizes were obtained. Using Lüscher’s formula, the corresponded phase shifts were calculated. Then, we compared the infinite volume phase shifts with the finite volume phase shifts acquired by Lüscher’s formula. Description: Extent: 7p. Sat, 31 Dec 2011 13:30:00 GMT http://hdl.handle.net/2440/77618 2011-12-31T13:30:00Z http://hdl.handle.net/2440/77617 Title: Baryon resonances and hadronic interactions in a finite volume Author: Hall, Jonathan Michael MacGillivray; Hsu, Anthony Chi-Pin; Leinweber, Derek Bruce; Thomas, Anthony William; Young, Ross Daniel Abstract: In a finite volume, resonances and multi-hadron states are identified by discrete energy levels. When comparing the results of lattice QCD calculations to scattering experiments, it is important to have a way of associating the energy spectrum of the finite-volume lattice with the asymptotic behaviour of the S-matrix. A new technique for comparing energy eigenvalues with scattering phase shifts is introduced, which involves the construction of an exactly solvable matrix Hamiltonian model. The model framework is applied to the case of ∆ → Nπ decay, but is easily generalized to include multi-channel scattering. Extracting resonance parameters involves matching the energy spectrum of the model to that of a lattice QCD calculation. The resulting fit parameters are then used to generate phase shifts. Using a sample set of pseudodata, it is found that the extraction of the resonance position is stable with respect to volume for a variety of regularization schemes, and compares favorably with the well-known Lüscher method. The model-dependence of the result is briefly investigated. Description: Extent: 7p. Sat, 31 Dec 2011 13:30:00 GMT http://hdl.handle.net/2440/77617 2011-12-31T13:30:00Z http://hdl.handle.net/2440/77616 Title: The influence of instantons on the quark propagator Author: Trewartha, Daniel; Kamleh, Waseem Rolf; Leinweber, Derek Bruce; Moran, Peter John Abstract: We use over-improved stout-link smearing to investigate the presence and nature of instantons on the lattice. We find that smearing can remove short-range effects with little damage to the longrange structure of the gauge field, and that after around 50 sweeps this process is complete. There are more significant risks for very high levels of smearing beyond 100 sweeps. We are thus able to produce gauge configurations dominated by instanton effects. We then calculate the overlap quark propagator on these configurations, and thus the non-perturbative mass function. We find that smeared configurations preserve the majority of dynamical mass generation, and conclude that instantons are primarily responsible for the dynamical generation of mass. Description: Extent: 6p. Sat, 31 Dec 2011 13:30:00 GMT http://hdl.handle.net/2440/77616 2011-12-31T13:30:00Z http://hdl.handle.net/2440/77615 Title: Scale setting, sigma terms and the Feynman-Hellman theorem Author: Shanahan, Phiala Elisabeth; Thomas, Anthony William; Young, Ross Daniel Abstract: The authors recently presented new values for the octet baryon sigma terms. These were extracted using the Feynman-Hellman theorem from a chiral perturbation theory fit to octet baryon mass data from the PACS-CS collaboration. Of particular interest is the precise determination of the strangeness sigma term δs = 21±6 MeV. In this work, we elaborate on the critical effect which the choice of scale setting has on this value. We discuss the prospect that the comparison of direct and 'spectrum' determinations of the sigma terms from the lattice can provide insight not only into scale setting on the lattice, but into QCD itself. Description: Extent: 7p. Sat, 31 Dec 2011 13:30:00 GMT http://hdl.handle.net/2440/77615 2011-12-31T13:30:00Z