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Despite its success, the Standard Model (SM) of particle physics fails to explain certain observations, such as the baryon asymmetry in the universe, dark matter, or neutrino masses. We are interested in indirect searches for physics beyond the SM, conducted in low-energy experiments at very high precision. These observables pose interesting theoretical challenges concerning the model-independent description of effects beyond the SM, as well as non-perturbative effects due to the strong nuclear force.
Provided that physics beyond the SM consists of heavy particles, their indirect quantum effects on low-energy observables can be described in a model-independent way in terms of effective field theories, which are the SMEFT above and the LEFT below the electroweak scale. Our work aims at the extension of these theories to higher orders and the consistent inclusion of threshold effects.
Beyond-the-SM sources of CP or lepton-flavor violation are probed up to very high scales by searches for electric dipole moments or lepton-flavor-violating decay processes, e.g., in the upcoming n2EDM and Mu3e experiments at PSI. We are interested in non-perturbative effects that affect these observables at low energies. Their description is based on effective field theories and usually requires input from lattice QCD.
The current SM prediction of the anomalous magnetic moment of the muon has been summarized in the white paper of the Muon g-2 Theory Initiative. The theoretical uncertainty is dominated by hadronic contributions, i.e., effects of the strong interaction, in particular hadronic vacuum polarization and hadronic light-by-light scattering. The white-paper prediction differs from the current experimental value by 5.1σ. However, since the publication of the white paper, several puzzles have emerged in the theoretical prediction that are not yet understood, in particular the tension between lattice QCD and data input, as well as inconsistencies between different data sets. We are working on reducing the hadronic uncertainties using dispersion relations, which are based on the principles of unitarity and analyticity.
