Ground state for point particles interacting through a massless scalar   Bose field
  We consider a massless scalar Bose field interacting with two particles, one of them infinitely heavy. Neither an infrared nor an ultraviolet cutoff is imposed. In case the charge of the particles is of the same sign and sufficiently small, we prove the existence of a ground state. 
Masao Hirokawa, Fumio Hiroshima and Herbert Spohn