Tests of Improved Kogut-Susskind Fermion Actions

Improvements of the Kogut-Susskind quark action may allow extraction of continuum physics from coarser lattices than would be required with the simplest formulation. This is especially important for full QCD simulations, which are much more time consuming than quenched calculations. Improvement of the rotational symmetry and the dispersion relation can be achieved by introducing the Naik term, a coupling to third nearest neighbors. A more severe problem is flavor symmetry breaking, which is large for the currently accessible lattice spacings. It has been shown that smearing of the gauge links reduces flavor symmetry breaking. This is because smearing reduces the coupling to high transverse momentum gluons which cause transitions among the corners of the Brillouin zone. There are various smearings proposed so far. The simplest one, which has been studied by the MILC collaboration [1], is the introduction of the 3-link staple to the coupling of the nearest neighbors. A more extensive smearing has been studied by Sinclair and Lagae [2], who have shown that flavor symmetry breaking is further reduced. Finally, extensive APE smearing has been studied in SU(2) quenched spectroscopy [3], showing degeneracy within statistical errors between the Goldstone pion and the local non-Goldstone pion (π2). In this paper, we study the effects of several types of smearing on the flavor symmetry break-