Spectral Theory near Thresholds for Weak Interactions with Massive   Particles
  We consider a Hamiltonian describing the weak decay of the massive vector boson Z0 into electrons and positrons. We show that the spectrum of the Hamiltonian is composed of a unique isolated ground state and a semi-axis of essential spectrum. Using a suitable extension of Mourre's theory, we prove that the essential spectrum below the boson mass is purely absolutely continuous. 
Jean-Marie Barbaroux, J\'er\'emy Faupin and Jean-Claude Guillot
math-ph math.MP math.SP