Non-Perturbative Calculation of the Scalar Yukawa Theory in Four-Body   Truncation
  The quenched scalar Yukawa theory is solved in the light-front Tamm-Dancoff approach including up to four constituents (one scalar nucleon, three scalar pions). The Fock sector dependent renormalization is implemented. By studying the Fock sector norms, we find that the lowest two Fock sectors dominate the state even in the large-coupling region. The one-body sector shows convergence with respect to the Fock sector truncation. However, the four-body norm exceeds the three-body norm at the coupling $\alpha \approx 1.7$. 
Yang Li, V. A. Karmanov, P. Maris, James P. Vary
nucl-th