Improving the lattice QCD Hamiltonian

Following the procedure of Lepage, first a classically improved Kogut Susskind Hamiltonian is derived using a transfer matrix or Legendre transformation method. In this formulation, the color electric energy becomes an infinite series with long range terms. This deficiency can be cured by arguing with the non-uniqueness of the classically improved action yielding the result that the same order of improvement can be acieved by keeping only nearest neighbor interactions. A further tadepole improvement of the Hamiltonian may be introduced straightforwardly. A final improvement involves a (Hamiltonian) perturbative calculation of suitable observables. An incorporation of the improved Hamiltonian into a coupled cluster calculation of the spectrum is possible and should allow to obtain reliable results for the glueball spectrum in lower order than with the original Kogut Susskind Hamiltonian. (orig.)