Speaker
Description
The purely leptonic FCNC decays $B_{s,d} \to \ell^+ \ell^-$ are powerful probes of the CKM picture of the SM and due to helicity suppression are very sensitive to NP contributions. The hadronic uncertainties are under exceptionally good control due to lattice calculations, allowing theoretical control at the percent level thereby neglecting currently QED corrections. This gap can be closed for this particularly simple decay into muons. We present the calculation of the leading power-enhanced structure-dependent virtual QED corrections and their combination with real radiation from first principles for the case when the energy of the undetected photons is small compared to the QCD binding energy and the muon mass. The QED logarithms that involve the process-specific scales are factorized and resummed with the help of soft-collinear effective theory (SCET).
