Abstract
We discuss a simple renormalisable, gauge invariant model with a fermiophobic $Z'$ boson: it has no couplings to the three Standard Model (SM) chiral families, but does couple to a fourth vector-like (VL) family. The SM Higgs couples to the fourth VL lepton, leading to an enhanced contribution to the muon anomalous magnetic moment $\left(g-2\right)_{\mu}$. The latter contribution requires a non-vanishing coupling of $Z'$ to right-handed muons, which arises within this model due to mixing effects between the SM and VL fermions, along with $Z'$ couplings to the second generation SM lepton doublet and third generation SM quark doublet. This model can simultaneously account for the measured $B$-decay ratios $R_{K^{(*)}}$ and $\left(g-2\right)_{\mu}$. We identify the parameter space where this explanation is consistent with existing experimental constraints coming from $B_{s}-\bar{B}_{s}$ mixing, neutrino trident production and collider searches. We also check that the SM Higgs coupling to the fourth VL lepton does not produce a dangerous contribution to the Higgs diphoton decay.
Highlights
The vast majority of particle-physics data is consistent with the predictions of the Standard Model (SM), in recent times a conspicuous series of discrepancies in flavor observables has been established
III, we show how it is possible to switch on the couplings of the Z0 to the muon and bs-quarks through mixing with the VL fermions, thereby eliminating all unnecessary couplings and allowing us to focus on the connection between the RKðÃÞ and ðg − 2Þμ anomalies
We have shown that both muon anomalies RKðÃÞ and ðg − 2Þμ can be simultaneously addressed in a simplified fermiophobic Z0 model with 75 GeV ≲ MZ0 ≲ 2 TeV
Summary
The vast majority of particle-physics data is consistent with the predictions of the Standard Model (SM), in recent times a conspicuous series of discrepancies in flavor observables has been established. The fact that the latest phenomenological analyses [23,24] leave the possibility to include an effective operator sLγμbLμRγμμR in the explanation of RKðÃÞ opens the possibility to explain simultaneously RKðÃÞ and ðg − 2Þμ within this Z0 model It has to be checked whether such simultaneous explanation of both anomalies can preserve all currently released high energy experimental data, such as the measurement of the mass difference ΔMs of neutral Bs mesons, the observations of neutrino trident production and the most recent collider signatures. The models in [64,65] are similar model to that considered here but with general mixing between VL and SM fermions, which leads to a large number of parameters, including all possible Z0 couplings to SM fermion, along with dangerous FCNCs and Z − Z0 kinetic mixing Such a framework makes it difficult to systematically explore the parameter space, and instead a search of best fit points is performed.
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