Generic loop effects of new scalars and fermions in b → sℓ+ℓ− and a vector-like 4th generation

Abstract

In this article we investigate in detail the possibility of accounting for the b → s + − anomalies via box contributions involving with new scalars and fermions. For this purpose, we first write down the most general Lagrangian which can generate the desired effects and then calculate the generic expressions for all relevant b → s Wilson coefficients. Here we extend previous analysis by allowing that the new particles can also couple to right-handed Standard Model (SM) fermions as preferred by recent b → s + − data and the anomalous magnetic moment of the muon. In the second part of this article we illustrate this generic approach for a UV complete model in which we supplement the Standard Model by a 4 th generation of vector-like fermions and a real scalar field. This model allows one to coherently address the observed anomalies in b → s + − transitions and in a µ without violating the bounds from other observables (in particular B s −B s mixing) or LHC searches. In fact, we find that our global fit to this model, after the recent experimental updates, is very good and prefers couplings to right-handed SM fermions, showing the importance of our generic setup and calculation performed in the first part of the article.

∆Ms theory precision confronts flavour anomalies

“…On the other hand, the recent update of R K at Moriond 2019 [42] favours a non-zero RH quark current contribution, as widely discussed in the literature since then (see e.g. [54][55][56][57][58][59][60]). There is however a problem with this solution, which is that in our Z model, at the leading order in the NP contribution, the behaviour can be written as has shrunk by only a small amount, and so our benchmark point is only marginally more favoured.…”

“…Intriguingly, one obtains a very good description of the b → s data by allowing new physics only in a single combination of Wilson coefficients (for recent fits see e.g. [54][55][56][57][58][59][60]). The best-fit scenario δC µ 9 = −δC µ 10 ≈ −0.53 ± 0.08 of [54] corresponds to an effective operator with left-handed (LH) quark and muon currents and we consider its interplay with ∆M s in Section 3.4.…”

Explaining b→sℓ+ℓ− data by sneutrinos in the R -parity violating MSSM

“…(3) can lead to a valuable effect. These interactions are similar to but different from the generic [49]. In our work the fermions Ψ A represent the SM down type quarks rather than new particles, and the interactions with charged leptons are provided by R-parity conserving MSSM.…”

Complete vectorlike fourth family with U(1)′ : A global analysis

“…[2][3][4][5]. The b → s + − anomaly is addressed by introducing a Z boson [6][7][8][9] and new particles which induce box diagram contributions [10][11][12][13][14][15][16][17][18]. Both anomalies can be explained simultaneously in models with VL fermions and a Z boson [19][20][21][22][23].…”