Spectral problems about many-body Dirac operators mentioned by   Derezi\'{n}ski
  We consider spectral problems for many-body Dirac operators mentioned by Derezi\'{n}ski in the IAMP News Bulletin of January 2012. In particular, we derive a representation of the Dirac Coulomb operator for a helium-like ion as a matrix operator of order sixteen. We show that it is essentially self-adjoint (under natural restrictions on the coupling constants), that the essential spectrum of its closure is the whole real line and that it has no eigenvalues. 
Takashi Okaji, Hubert Kalf and Osanobu Yamada
math.AP math.SP