Enhanced binding of an N-particle system interacting with a scalar field   II.Relativistic version
  An enhanced binding of $N$-{\it relativistic} particles coupled to a massless scalar bose field is investigated. It is not assumed that the system has a ground state for the zero-coupling. It is shown, however, that there exists a ground state for sufficiently large coupling. The proof is based on checking the stability condition and showing a uniform exponential decay of infrared regularized ground states. 
Fumio Hiroshima and Itaru Sasaki
math-ph math.MP