We study the ground state energy and ground states of systems coupling nonrelativistic
quantum particles and force-carrying Bose fields, such as radiation, in the quasiclassical
approximation. The latter is very useful whenever the force-carrying field has a very large
number of excitations and thus behaves in a semiclassical way, while the nonrelativistic
particles, on the other hand, retain their microscopic features. We prove that the ground state
energy of the fully microscopic model converges to that of a nonlinear quasiclassical …