On the Nonrelativistic Limit of the phi^4 Theory in 2+1 Dimensions
  We study the nonrelativistic limit of the quantum theory of a real scalar field with quartic self-interaction. The two body scattering amplitude is written in such way as to separate the contributions of high and low energy intermediary states. From this result and the two loop computation of the self energy correction, we determine an effective nonrelativistic action. 
M. Gomes, J. M. C. Malbouisson, and A. J. da Silva