Importance of Loop Effects in Explaining the Accumulated Evidence for New Physics in B Decays with a Vector Leptoquark

Computing tools for effective field theories: SMEFT-Tools 2022 Workshop Report, 14-16th September 2022, Zürich

In recent years, theoretical and phenomenological studies with effective field theories have become a trending and prolific line of research in the field of high-energy physics. In order to discuss present and future prospects concerning automated tools in this field, the SMEFT-Tools 2022 workshop was held at the University of Zurich from 14th-16th September 2022. The current document collects and summarizes the content of this workshop.

Confronting the vector leptoquark hypothesis with new low- and high-energy data

In light of new data we present an updated phenomenological analysis of the simplified U 1 -leptoquark model addressing charged-current B-meson anomalies. The analysis shows a good compatibility of low-energy data (dominated by the lepton flavor universality ratios R D and R D ∗ ) with the high-energy constraints posed by p p → τ τ ¯ Drell-Yan data. We also show that present data are well compatible with a framework where the leptoquark couples with similar strength to both left- and right-handed third-generation fermions, a scenario that is well-motivated from a model building perspective. We find that the high-energy implications of this setup will be probed at the 95% confidence level in the high-luminosity phase of the LHC.

New physics in rare B decays after Moriond 2021

The anomalies in rare B decays endure. We present results of an updated global analysis that takes into account the latest experimental input - in particular the recent results on R K and BR ( B s → μ + μ - ) - and that qualitatively improves the treatment of theory uncertainties. Fit results are presented for the Wilson coefficients of four-fermion contact interactions. We find that muon specific Wilson coefficientsC 9 ≃ - 0.73 orC 9 = - C 10 ≃ - 0.39 continue to give an excellent description of the data. If only theoretically clean observables are considered, muon specificC 10 ≃ 0.60 orC 9 = - C 10 ≃ - 0.35 improve over the Standard Model byΔ χ 2 ≃ 4.7 σ andΔ χ 2 ≃ 4.6 σ , respectively. In various new physics scenarios we provide predictions for lepton flavor universality observables and CP asymmetries that can be tested with more data. We update our previous combination of ATLAS, CMS, and LHCb data on BR ( B s → μ + μ - ) and BR ( B 0 → μ + μ - ) taking into account the full two-dimensional non-Gaussian experimental likelihoods.

B Discrepancies Hold Their Ground

This write-up aims at a comprehensive discussion of the status of the so-called B-anomalies, as well as their interpretation from an effective-theory point of view. The focus is on presenting facts and physics arguments using the bare minimum of equations and pointing instead to the relevant literature in each specific case.

Combined Explanation of the Z→bb[over ¯] 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→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]).