Improving flavor symmetry in the Kogut-Susskind hadron spectrum
  We study the effect of modifying the coupling of Kogut-Susskind quarks to the gauge field by replacing the link matrix in the quark action by a "fat link", or sum of link plus three-link paths. Flavor symmetry breaking, determined by the mass difference between the Goldstone and non-Goldstone local pions, is reduced by approximately a factor of two by this modification. 
Tom Blum, Carleton DeTar, Steven Gottlieb, Urs M. Heller, James E.   Hetrick, Kari Rummukainen, R.L. Sugar, Doug Toussaint, ...