Journal of High Energy Physics

, 2018:75 | Cite as

Third family hypercharge model for \( {R}_{K^{\left(\ast \right)}} \) and aspects of the fermion mass problem

  • B. C. Allanach
  • Joe DavighiEmail author
Open Access
Regular Article - Theoretical Physics


We present a model to explain LHCb’s recent measurements of RK and \( {R}_{K^{\left(\ast \right)}} \) based on an anomaly-free, spontaneously-broken U(1)F gauge symmetry, without any fermionic fields beyond those of the Standard Model (SM). The model explains the hierarchical heaviness of the third family and the smallness of quark mixing. The U(1)F charges of the third family of SM fields and the Higgs doublet are set equal to their respective hypercharges. A heavy Z′ particle with flavour-dependent couplings can modify the \( \left[\overline{b_L}{\gamma}^{\rho }{s}_L\right]\left[\overline{\mu_L}{\gamma}_{\rho }{\mu}_L\right] \) effective vertex in the desired way. The Z′ contribution to \( {B}_s-\overline{B_s} \) mixing is suppressed by a small mixing angle connected to Vts, making the constraint coming from its measurement easier to satisfy. The model can explain RK and \( {R}_{K^{*}} \) whilst simultaneously passing other constraints, including measurements of the lepton flavour universality of Z couplings.


Beyond Standard Model Quark Masses and SM Parameters Heavy Quark Physics 


Open Access

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© The Author(s) 2018

Authors and Affiliations

  1. 1.DAMTPUniversity of CambridgeCambridgeUnited Kingdom

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