We derive Hamiltonian flow equations giving the evolution of the Lipkin
Hamiltonian to a diagonal form using continuous unitary transformations. To
close the system of flow equations, we present two different schemes. First we
linearize an operator with three pairs of creation and destruction operators by
reducing it to the z component of the quasi spin. We obtain the well known
RPA-result in the limit of large particle number. In the second scheme we
introduce a new operator which improves the resulting spectrum considerably
especially for few particles.Comment: 10 pages, 2 eps figures, uses article.sty, epsfig.st
