====== C3b: New Physics models for flavour observables ======

^Principal Investigator ^^
|[[https://www.ttp.kit.edu/en/memberpages/nierste | 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 ====

  - Multi-Higgs doublet models with heavy Higgses
    * devise extended Higgs sectors to alleviate flavour anomalies 
    * improve $B_c$ lifetime constraint
    * predict branching fraction for $h\to \tau \mu$
  - 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
  - $\mathbf{b\to s \ell^+\ell^-}$ 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
  - Flavour and supersymmetry
    * study hierarchical squark masses  enhancing FCNC transitions
    * construct a supersymmetric SU(2)$_L\times$SU(2)$_R$ model
  - 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