On the Essential Spectrum of Many-Particle Pseudorelativistic   Hamiltonians with Permutational Symmetry Account
  In this paper we formulate our results on the essential spectrum of many-particle pseudorelativistic Hamiltonians without magnetic and external potential fields in the spaces of functions, having arbitrary type $\alpha$ of the permutational symmetry. We discover location of the essential spectrum for all $\alpha$ and for some cases we establish new properties of the lower bound of this spectrum, which are useful for study of the discrete spectrum. 
Grigorii Zhislin