Rare semileptonic processes, i.e. processes in which both quarks and leptons participate and are obscured by the structure of quark or lepton flavors, play a key role both in understanding and verifying the predictions of the standard theory of elementary particles, and in searching for possible signals of new physics beyond the standard model. In the last decade, special attention has been paid to the phenomenon of universality of lepton flavors, i.e. that among the fundamental forces in Nature, only the Higgs interaction distinguishes between flavors of charged leptons. Increased interest has been fueled by experimental hints that violations of leptonic universality in (rare) semileptonic decays of B mesons are larger than predicted within the standard theoretical framework.
An important aspect of understanding semileptonic processes is the intertwining of the effects of the weak and strong interactions. The achievable accuracy of measurements of these processes as well as their theoretical predictions are often crucially limited by our quantitative understanding and description of the relevant strong interactions that bind quarks into long-lived hadronic states. At sufficiently high energies, the relevant dynamics can be described by perturbative expansion in the coupling constant of strong interactions, but at low energies we have to resort to numerical calculations, for example in the form of simulations of quantum chromodynamics on a lattice.
The research training program will address some open questions related to the effects of short- and long-range strong interactions on rare semileptonic processes, both at low energies, in the form of rare (semi)leptonic hadron decays, as well as on the direct production of particles in high-energy particle colliders such as the LHC and the possible future FCC-ee collider at CERN, as well as in cosmic rays. The emphasis will be on processes that could shed light on the puzzle (violation of universality) of lepton flavors, e.g. where heavy leptons (mu, tau) and quarks (t,b) and neutrinos participate in them. At the same time, some of them have not been detected experimentally until now, or the accuracy of their measurements is expected to improve significantly in future planned experiments.