On the renormalization of Hamiltonians

We introduce a novel method for the renormalization of the Hamiltonian oper ator in Quantum Field Theory in the spirit of the Wilson renormalization gr oup. By a series of unitary transformations that successively decouples the high-frequency degrees of freedom and partially diagonalizes the high-ener gy part, we obtain the effective Hamiltonian for the low energy degrees of freedom. We successfully apply this technique to compute the 2-loop renorma lized Hamiltonian in scalar lambda phi(4) theory. (C) 1999 Elsevier Science B.V. All rights reserved.