Resonances in nonrelativistic QED
(by Volker Bach)
It is shown that in the standard model of
nonrelativstic matter interacting with the quantized
radiation field excited atomic or molecular energy
levels turn into resonances with a finite life-time
which, to leading order in the coupling constant,
can be estimated by second-order perturbation theory.
The proof of this statement employs some standard tools,
like complex dilation, but also some nonstandard ones
in this context, like the renormalization group based
on the smooth Feshbach map.
Most of what is presented is joint work with J. Froehlich
and I. M. Sigal.