Hydrogen-like atoms in relativistic QED

TL;DR

This paper reviews relativistic quantum electrodynamics models of hydrogen-like atoms, establishing fundamental spectral properties, ground state existence, and localization results for various potentials and parameters.

Contribution

It provides a comprehensive analysis of two relativistic models of hydrogenic atoms in QED, including spectral properties and ground state existence, with results valid for broad parameter ranges.

Findings

Hamiltonians are semi-bounded and have positive ionization energy

Existence of degenerate ground states at the spectrum's bottom

Results hold for arbitrary fine-structure constants and general potentials

Abstract

In this review we consider two different models of a hydrogenic atom in a quantized electromagnetic field that treat the electron relativistically. The first one is a no-pair model in the free picture, the second one is given by the semi-relativistic Pauli-Fierz Hamiltonian. For both models we discuss the semi-boundedness of the Hamiltonian, the strict positivity of the ionization energy, and the exponential localization in position space of spectral subspaces corresponding to energies below the ionization threshold. Moreover, we prove the existence of degenerate ground state eigenvalues at the bottom of the spectrum of the Hamiltonian in both models. All these results hold true, for arbitrary values of the fine-structure constant and the ultra-violet cut-off, and for a general class of electrostatic potentials including the Coulomb potential with nuclear charges less than (sometimes including) the critical charges without radiation field. Apart from a detailed discussion of diamagnetic inequalities in QED (which are applied to study the semi-boundedness) all results stem from earlier articles written by the authors. While a few proofs are merely sketched, we streamline earlier proofs or present alternative arguments at many places.