Javier Virto

Global analysis of b → sℓℓ anomalies

A bstractWe present a detailed discussion of the current theoretical and experimental situation of the anomaly in the angular distribution of B → K*(→ Kπ)μ+μ−, observed at LHCb in the 1 fb−1 dataset and recently confirmed by the 3 fb−1 dataset. The impact of this data and other recent measurements on b → sℓ+ℓ− transitions (ℓ = e, μ) is considered. We review the observables of interest, focusing on their theoretical uncertainties and their sensitivity to New Physics, based on an analysis employing the QCD factorisation approach including several sources of hadronic uncertainties (form factors, power corrections, charm-loop effects). We perform fits to New Physics contributions including experimental and theoretical correlations. The solution that we proposed in 2013 to solve the B → K*μ+μ− anomaly, with a contribution C9NP≃−1

Non-abelian gauge extensions for B-decay anomalies

{mathcal{C}}_9^{mathrm{NP}}simeq -1

Three-body non-leptonic B decays and QCD factorization

, is confirmed and reinforced. A wider range of New-Physics scenarios with high significances (between 4 and 5 σ) emerges from the fit, some of them being particularly relevant for model building. More data is needed to discriminate among them conclusively. The inclusion of b → se+e− observables increases the significance of the favoured scenarios under the hypothesis of New Physics breaking lepton flavour universality. Several tests illustrate the robustness of our conclusions.

Theoretical status of

A bstractThe recent LHCb angular analysis of the exclusive decay B → K*μ+μ− has indicated significant deviations from the Standard Model expectations. Accurate predictions can be achieved at large K*-meson recoil for an optimised set of observables designed to have no sensitivity to hadronic input in the heavy-quark limit at leading order in αs. However, hadronic uncertainties reappear through non-perturbative ΛQCD/mb power corrections, which must be assessed precisely. In the framework of QCD factorisation we present a systematic method to include factorisable power corrections and point out that their impact on angular observables depends on the scheme chosen to define the soft form factors. Associated uncertainties are found to be under control, contrary to earlier claims in the literature. We also discuss the impact of possible non-factorisable power corrections, including an estimate of charm-loop effects. We provide results for angular observables at large recoil for two different sets of inputs for the form factors, spelling out the different sources of theoretical uncertainties. Finally, we comment on a recent proposal to explain the anomaly in B → K*μ+μ− observables through charm-resonance effects, and we propose strategies to test this proposal identifying observables and kinematic regions where either the charm-loop model can be disentangled from New Physics effects or the two options leave different imprints.

B \to K^* \mu^+\mu^-

Abstract We study the generic features of minimal gauge extensions of the Standard Model in view of recent hints of lepton-flavor non-universality in semi-leptonic b → s l + l − and b → c l ν decays. We classify the possible models according to the symmetry-breaking pattern and the source of flavor non-universality. We find that in viable models the S U ( 2 ) L factor is embedded non-trivially in the extended gauge group, and that gauge couplings should be universal, hinting to the presence of new degrees of freedom sourcing non-universality. Finally, we provide an explicit model that can explain the B -decay anomalies in a coherent way and confront it with the relevant phenomenological constraints.

: The path towards New Physics

A bstractThe B → K∗μμ decay exhibits deviations with respect to Standard Model expectations and the measurement of the ratio RK hints at a violation of lepton-flavour universality in B → Kℓℓ transitions. Both effects can be understood in model-independent fits as a short-distance contribution to the Wilson coefficient C9μ, with some room for similar contributions in other Wilson coefficients for b → sμμ transitions. We discuss how a full angular analysis of B → K∗ee and its comparison with B → K∗μμ could improve our understanding of these anomalies and help confirming their interpretation in terms of short-distance New Physics. We discuss several observables of interest in this context and provide predictions for them within the Standard Model as well as within several New Physics benchmark scenarios. We pay special attention to the sensitivity of these observables to hadronic uncertainties from SM contributions with charm loops.

Time dependence in B → V ℓℓ decays

Abstract We extend the framework of QCD factorization to non-leptonic B decays into three light mesons, taking as an example the decay B + → π + π + π − . We discuss the factorization properties of this decay in different regions of phase space. We argue that, in the limit of very large b -quark mass, the central region of the Dalitz plot can be described in terms of the B → π form factor and the B and π light-cone distribution amplitudes. The edges of the Dalitz plot, on the other hand, require different non-perturbative input: the B → π π form factor and the two-pion distribution amplitude. We present the set-up for both regions to leading order in both α s and Λ QCD / m b and discuss how well the two descriptions merge. We argue that for realistic B -meson masses there is no perturbative center in the Dalitz plot, but that a systematic description might be possible in the context of two-pion states. As an example, we estimate the B → ρ π branching fraction beyond the quasi-particle approximation. We also discuss the prospects for studies of three-body and quasi-two-body non-leptonic B decays from QCD.

Four-body contributions to

We summarize the status of the analysis of the 4-body angular distribution B → K*(→ Kπ)μ+μ- using a basis of optimized observables. We provide a New Physics interpretation of the pattern of deviations observed in the 1fb-1 dataset with the coefficient of the semileptonic operator O9 being the main responsible for this pattern. Also other scenarios involving more Wilson coefficients are briefly discussed. Further, we present a detailed description of each of the hadronic uncertainties entering our predictions and suggest possible tests for alternative hadronic explanations. Our most accurate SM predictions for the optimized observables in various bins including all uncertainties are also provided.