Formulation of few-body equations without partial waves

A formalism is developed whereby the two-body Lippmann-Schwinger equation may be solved in momentum space without partial-wave decomposition. The integral equation derived is two-dimensional and so is amenable to direct numerical solution. Because the technique uses the well-known helicity formalism, the matrices involved can be further reduced by taking advantage of symmetries common in nuclear and atomic systems (parity conservation, particle symmetry). An example is shown for nucleon-nucleon scattering, and the results are compared to those obtained from the usual partial-wave method.