  We consider a Hamiltonian with cutoffs describing the weak decay of spin one
massive bosons into the full family of leptons. The Hamiltonian is a
self-adjoint operator in an appropriate Fock space with a unique ground state.
We prove a Mourre estimate and a limiting absorption principle above the ground
state energy and below the first threshold for a sufficiently small coupling
constant. As a corollary, we prove absence of eigenvalues and absolute
continuity of the energy spectrum in the same spectral interval.
