Higher Fock sectors in Wick-Cutkosky model
  In the Wick-Cutkosky model we analyze nonperturbatively, in light-front dynamics, the contributions of two-body and higher Fock sectors to the total norm and electromagnetic form factor. It turns out that two- and three-body sectors always dominate. For maximal value of coupling constant $\alpha=2\pi$, corresponding to zero bound state mass M=0, they contribute 90% to the norm. With decrease of $\alpha$ the two-body contribution increases up to 100%. The form factor asymptotic is always determined by two-body sector. 
V.A. Karmanov and Dae Sung Hwang