Four-Body Bound State Formulation in Three-Dimensional Approach (Without   Angular Momentum Decomposition)
  The four-body bound state with two-body forces is formulated by the Three-Dimensional approach, which greatly simplifies the numerical calculations of few-body systems without performing the Partial Wave components. We have obtained the Yakubovsky equations directly as three dimensional integral equations. 
M. R. Hadizadeh and S. Bayegan