Free from spurious solutions integral equation for three-magnon bound   states in 1D XXZ ferromagnet
  A new integral equation for three-magnon bound states in XXZ spin chain is suggested. Unlike the one presented by C. K. Majumdar about 40 years ago this equation does not have spurious solutions. Such an advantage is a result of decomposition of the wave function in the Bloch basis rather than in the basis of flat waves. 
P. N. Bibikov
cond-mat.str-el