C3b: New Physics models for flavour observables

Principal Investigator
Prof. Ulrich Nierste Karlsruhe Institute of Technology


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
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