Abstract

We consider the non- and semi-relativistic Pauli-Fierz models for a single electron in an electrostatic potential interacting with the quantized radiation field. We prove that the ability of the system to bind the electron is enhanced in both models in the sense that coupling constant thresholds for certain classes of weak potentials are strictly decreased by the radiation field. Furthermore, we show that binding energies are always increased by the radiation field. The new achievementis that the occurrence of these effects is established, for arbitrary large values of the fine-structure constant and the ultra-violet cutoff. As a byproduct we determine the leading asymptotics of the ground state energy of the free, translation invariant semi-relativistic Pauli-Fierz Hamiltonian,as the ultra-violet cutoff goes to infinity.