Abstract
In this Letter, we propose a simple model that can provide a combined explanation of the Z→bb[over ¯] forward-backward asymmetry, the Cabibbo angle anomaly (CAA), τ→μνν and b→sℓ^{+}ℓ^{-} data. This model is obtained by extending the standard model (SM) by two heavy vectorlike quarks (an SU(2)_{L} doublet (singlet) with hypercharge -5/6 (-1/3), two new scalars (a neutral and a singly charged one), and a gauged L_{μ}-L_{τ} symmetry. The mixing of the new quarks with the SM ones, after electroweak symmetry breaking, does not only explain Z→bb[over ¯] data, but also generates a lepton flavor universal contribution to b→sℓ^{+}ℓ^{-} transitions. Together with the lepton flavor universality violating effect, generated by loop-induced Z^{'} penguins involving the charged scalar and the heavy quarks, it gives an excellent fit to data (6.1σ better than the SM). Furthermore, the charged scalar (neutral vector) gives a necessarily constructive tree-level (loop) effect in μ→eνν (τ→μνν), which can naturally account for the CAA (Br[τ→μνν]/Br[τ→eνν] and Br[τ→μνν]/Br[μ→eνν]).
Highlights
Combined Explanation of the Z → bb Forward-Backward Asymmetry, the Cabibbo Angle Anomaly, and τ → μνν and b → sl + l − Data
In this Letter, we propose a simple model that can provide a combined explanation of the Z → bbforward-backward asymmetry, the Cabibbo angle anomaly (CAA), τ → μνν and b → slþl− data
This model is obtained by extending the standard model (SM) by two heavy vectorlike quarks (an SUð2ÞL doublet with hypercharge −5=6 (−1=3), two new scalars, and a gauged Lμ − Lτ symmetry
Summary
CERN Theory Division, CH–1211 Geneva 23, Switzerland; Paul Scherrer Institut, CH–5232 Villigen PSI, Switzerland and Physik-Institut, Universität Zürich, Winterthurerstrasse 190, CH–8057 Zürich, Switzerland. In this Letter, we propose a simple model that can provide a combined explanation of the Z → bbforward-backward asymmetry, the Cabibbo angle anomaly (CAA), τ → μνν and b → slþl− data. This model is obtained by extending the standard model (SM) by two heavy vectorlike quarks (an SUð2ÞL doublet (singlet) with hypercharge −5=6 (−1=3), two new scalars (a neutral and a singly charged one), and a gauged Lμ − Lτ symmetry. Together with the lepton flavor universality violating effect, generated by loop-induced Z0 penguins involving the charged scalar and the heavy quarks, it gives an excellent fit to data (6.1σ better than the SM). The anomaly in b → slþl− data is accompanied by additional hints for the violation of LFU that are very interesting, even though they are statistically less significant: (i) RðDðÃÞÞ [85,86,87,88,89,90] points toward τ − μ LFU violation with a significance of > 3σ [91,92,93,94,95], (ii) the anomalous magnetic moment of the muon aμ [96] prefers NP coupling to muons by 3.7σ [97], (iii) Br1⁄2τ → μνν= Br1⁄2τ → eνν and Br1⁄2τ → μνν=Br1⁄2μ → eνν are indications for LFU violation with a significance of ≈2σ, and (iv) the deficit in first row Cabibbo-Kobayashi-Maskawa (CKM) unitarity, known as the Cabibbo angle anomaly (CAA), is at
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