  The technique of Hamiltonian flow equations is applied to the canonical
Hamiltonian of quantum electrodynamics in the front form and 3+1 dimensions.
  The aim is to generate a bound state equation in a quantum field theory,
particularly to derive an effective Hamiltonian which is practically solvable
in Fock-spaces with reduced particle number. The effective Hamiltonian,
obtained as a solution of flow eqautions to the second order, is solved
numerically for positronium spectrum. The impact of different similarity
functions is explicitly studied.
  The approach discussed can ultimately be used to address to the same problem
for quantum chromodynamics.

High Energy Physics - Theory