# C3b: New Physics models for flavour observables

Principal Investigator
Prof. Ulrich Nierste Karlsruhe Institute of Technology

### Subject

The phenomenological motivation of this project are the flavour anomalies, which are deviations between measurements and Standard-Model predictions in several observables. The most prominent flavour anomalies occur in $b\to s\mu^+\mu-$ and $b\to c\tau\nu$ decays, with statistical significances above $5\sigma$ and $4\sigma$, respectively. There are also tensions in the anomalous magnetic moment of the muon, $a_\mu$, and the measure of direct CP violation in $K\to\pi\pi$ decays, $\epsilon_K^\prime$. The project aims at explaining these anomalies in a coherent theory, which ideally will also address other shortcomings of the Standard Model. The focus will be on extended scalar sectors, supersymmetric theories, and models with extended gauge sectors. A common element of these model classes are additional Higgs fields, which naturally links this project to research area A.

### Project Topics

1. Multi-Higgs doublet models with heavy Higgses
• devise extended Higgs sectors to alleviate flavour anomalies
• improve $B_c$ lifetime constraint
• predict branching fraction for $h\to \tau \mu$
2. Multi-Higgs doublet models with a light neutral Higgs
• study light neutral pseudoscalar $\phi$ from broken flavour symmetries
• explore $B\to D^{(*)} \ell \nu \phi$ events in $B\to D^{(*)} \tau[\to\ell\nu\bar\nu] \nu$ data sample
3. $\mathbf{b\to s \ell^+\ell^-}$ and the flavour puzzle
• construct models of radiatively generated muon and electron masses containing large LFUV parameters needed to explain $R_{K^{(*)}}$
• $Z^\prime$ from gauged flavour symmetries
4. Flavour and supersymmetry
• study hierarchical squark masses enhancing FCNC transitions
• construct a supersymmetric SU(2)$_L\times$SU(2)$_R$ model
5. Pati-Salam and $\mathbf{E_6}$-inspired models
• study scalar leptoquarks of Pati-Salam Higgs sector
• construct $\mathbf{E_6}$-inspired models with $Z^\prime$ and vectorlike fermions