# PhD project: QED correction to rare and semileptonic B/D decays

## Project description

Quantum electrodynamic (QED) corrections to beauty  and  charm ($B$- and $D$-mesons) are by a large part in their infancy. Albeit the small fine structure constant such corrections can be sizeable because of non or partial cancellation of infrared divergences (large logarithms) between virtual and real emission diagrams (e.g. Kinoshita-Lee-Nauenberg theorem).
So far most/all approaches approximate the $B$-meson as an elementary particle with regards to the photon coupling. The aim of this thesis is to develop, together with the advisor, a framework where this can be overcome.

Besides being an interesting theoretical topic this is currently of particular relevance as  several ratios of observables of the type $R_K= \Gamma[B \to K \mu^+\mu^-]/\Gamma[B \to K e^+e^-]$ have shown deviations from the Standard Model predictions.These results challenge the Lepton Flavour Universality (LFU) principle of the Standard Model. https://cerncourier.com/a/beauty-quarks-test-lepton-universality/This has given rise to  speculations (in form research papers) about New Physics beyond the Standard Model which can be connected to other puzzles of particle physics such as the Dark Matter problem.Ratios such as $R_K$  are unique sensitive probes of the Standard Model (free from hadronic uncertainties) up to QED-corrections nota bene.

The aim of this thesis is to clarify these experimental results, which will see further improvement  by the LHCb- and  BelleII-experiment, within a new theoretical framework.