| Summary: | In this thesis I present results for the light hadron spectrum, light quark masses and meson decay constants from numerical simulations of lattice QCD. The simulations were performed on a 16<sup>3</sup> x 32 space-time lattice using the standard Wilson gauge field action and a fully <i>O</i>(<i>a</i>)-improved Sheikholeslami-Wohlert fermion action with <i>N<sub>j</sub> </i>= 2 degenerate flavours of dynamical fermions. A subset of these simulations were performed at fixed lattice spacing, as determined through the Sommer scale parameter, <i>r</i><sub>o</sub>, in order to investigate the effects associated with a finite sea quark mass whilst keeping cutoff and finite size effects fixed. A quenched simulation was also performed at this lattice spacing for comparative purposes. No clear evidence of unquenching was found in the light hadron spectrum at the quark masses used in the matched simulations studied here. Light quark masses were determined from chiral extrapolations of pseudoscalar and vector meson masses to both the standard and PCAC definitions of the quark mass. The bare strange quark mass was fixed through the <i>K</i>, <i>K*</i> and <i>ø </i>meson masses for comparison. Renormalised quark masses have been determined in the ? scheme at a reference scale of 2GeV with matching performed at two values of the scale parameter, <i>m </i>= 1/<i>a</i> and <i>m</i> = <i>p/a</i>, in order to study the systematic effects.
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