  22 years ago, Rebhan and van Nieuwenhuizen showed that loop corrections to
the mass of a quantum soliton depend on a choice of matching condition for the
regulators of the vacuum and one-soliton sector Hamiltonians. In supersymmetric
theories, regulators which preserve supersymmetry yield the correct quantum
corrections, as these are dictated by supersymmetry. However, in a general
theory it is not known which matching condition yields the correct mass. We use
the leading term in the operator that creates the soliton to construct the
regulated one-soliton sector Hamiltonian from that of the vacuum sector,
providing the correct matching condition. As an application, we derive a simple
formula for the one-loop mass of a kink in a large class of 1+1 dimensional
scalar field theories and also, at one loop, we diagonalize the Hamiltonian
which describes the kink excitations.
