Light-cone Hamiltonian flow for positronium
  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. 
Elena L. Gubankova, Hans-Christian Pauli, Franz J. Wegner, Gabor Papp