Seminarium "Teoria cząstek elementarnych i kosmologia"

I will discuss two examples of determinations of bound-state properties. First, a rare decay of positronium: in QED, its spin-0 state annihilates only into an even number of photons, and spin-1 into an odd number. I will show how these rules are broken by weak interactions. Next, modifications of the muon decay by binding in an atom will be presented. This is of current interest because of experiments COMET (J-PARC, Japan) and Mu2e (Fermilab, USA) that will use muonic aluminium to search for the lepton-flavor violating process in which muon is converted into an electron. In both cases disagreements with previously published results will be pointed out and explained.