Improved interpolating fields in the Schroedinger functional

Abstract

The general aim of this thesis is to probe several methods to extract low-energy quantities (masses, decay constants,...) more reliably in lattice gauge theory. We will investigate how to suppress contributions to correlation functions from the first excited meson state. We will show how to construct so-called improved meson interpolating fields, as they have only small contributions from the first excited meson state, from a basis of interpolating fields at the Schroedinger functional boundaries. The variational principle is applied to correlation matrices that are built up from boundary-to-boundary correlation functions. It will deliver information about the lowest-lying meson states in the considered channel. We also investigate the possibility to cancel the first excited state contribution by means of an alternative method. Moreover, an alternative way to extract the mass gap between the ground and the first excited state will be presented. Monte-Carlo simulations at several lattice spacings are performed in the 'quenched approximation'. Spectral properties of light-light and static-light pseudoscalar mesons are investigated. The first type is realised by two mass-degenerate quarks at about the strange quark mass, the second type by a light quark with the mass of the strange quark and an infinitely heavy b-quark. The light-light channel describes unphysically heavy pions and the static-light one is an approximation for the B_s-meson. The investigation of the latter case is particularly interesting since so-called B-factories, such as BaBar and Belle, are gathering physical information about masses, decay modes and CP-violating effects in the B-meson system. (orig.)SIGLEAvailable from: http://deposit.ddb.de/cgi-bin/dokserv?idn=972644628 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman