Lattice QCD Simulations of Baryon Spectra and Development of Improved Interpolating Field Operators

Large sets of baryon interpolating field operators are developed for use in lattice QCD studies of baryons with zero momentum. Because of the cubical discretization of space, the continuum rotational group is broken down to a finite point group. Operators are classified according to the irreducible representations of the double octahedral group. At first, three-quark quasi-local operators are constructed for each isospin and strangeness with suitable symmetry of Dirac indices. Nonlocal baryon operators are formulated in a second step as direct products of the quasi-local spinor structures together with lattice displacements. Appropriate Clebsch-Gordan coefficients of the octahedral group are used to form linear combinations of such direct products. The construction maintains maximal overlap with the continuum SU(2) group in order to provide a physically interpretable basis. Nonlocal operators provide direct couplings to states that have nonzero orbital angular momentum. Monte Carlo sim