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Search: authors:"Marco Nardecchia"

10 papers found.
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What is the scale of new physics behind the B-flavour anomalies?

Motivated by the recent hints of lepton flavour non-universality in B-meson semi-leptonic decays, we study the constraints of perturbative unitarity on the new physics interpretation of the anomalies in \(b \rightarrow c \ell \bar{\nu }\) and \(b \rightarrow s \ell \bar{\ell }\) transitions. Within an effective field theory approach we find that \(2 \rightarrow 2\) fermion ...

Flavour anomalies after the R K ∗ measurement

The LHCb measurement of the μ/e ratio R K ∗ indicates a deficit with respect to the Standard Model prediction, supporting earlier hints of lepton universality violation observed in the R K ratio. We show that the R K and R K ∗ ratios alone constrain the chiralities of the states contributing to these anomalies, and we find deviations from the Standard Model at the 4σ level. This ...

On the structure of anomalous composite Higgs models

We describe the anomaly structure of a composite Higgs model in which the SO(5) / SO(4) coset structure of the minimal model is extended by an additional, non-linearly realised \(U(1)_{\eta }\). In addition, we show that the effective Lagrangian admits a term that, like the Wess–Zumino–Witten term in the chiral Lagrangian for QCD, is not invariant under the non-linearly realised ...

Implications of perturbative unitarity for scalar di-boson resonance searches at LHC

We study the constraints implied by partial wave unitarity on new physics in the form of spin-zero di-boson resonances at LHC. We derive the scale where the effective description in terms of the SM supplemented by a single resonance is expected to break down depending on the resonance mass and signal cross section. Likewise, we use unitarity arguments in order to set perturbativity ...

Linear flavour violation and anomalies in B physics

We propose renormalizable models of new physics that can explain various anomalies observed in decays of B-mesons to electron and muon pairs. The new physics states couple to linear combinations of Standard Model fermions, yielding a pattern of flavour violation that gives a consistent fit to the gamut of flavour data. Accidental symmetries prevent contributions to baryon- and ...

Indirect constraints on the scalar di-photon resonance at the LHC

Motivated by the tantalizing excesses recently reported in the di-photon invariant mass spectrum at the LHC, we scrutinize some implications of scalar di-photon resonances in high energy proton-proton collisions. In particular, indications of a large width impose several challenges for model building. We show how calculability and unitarity considerations severely limit possible ...

Lepton flavor non-universality in B-meson decays from a U(2) flavor model

We address the recent anomalies in semi-leptonic B-meson decays using a model of fermion masses based on the U(2) flavor symmetry. The new contributions to b → sℓℓ transitions arise due to a tree-level exchange of a Z′ vector boson gauging a U(1) subgroup of the flavor symmetry. They are controlled by a single parameter and are approximately aligned to the Standard Model ...

Flavor and CP violation in Higgs decays

Flavor violating interactions of the Higgs boson are a generic feature of models with extended electroweak symmetry breaking sectors. Here, we investigate CP violation in these interactions, which can arise from interference of tree-level and 1-loop diagrams. We compute the CP asymmetry in flavor violating Higgs decays in an effective field theory with only one Higgs boson and in a ...

Accidental matter at the LHC

We classify weak-scale extensions of the Standard Model which automatically preserve its accidental and approximate symmetry structure at the renormalizable level and which are hence invisible to low-energy indirect probes. By requiring the consistency of the effective field theory up to scales of Λeff ≈ 1015 GeV and after applying cosmological constraints, we arrive at a finite ...

Hint of lepton flavour non-universality in B meson decays

The LHCb collaboration has recently presented their result on R K = ℬ(B + → K + μ + μ −)/ ℬ(B + → K + e + e −) for the dilepton invariant mass bin m ℓℓ 2 = 1 − 6 GeV2 (ℓ = μ, e). The measurement shows an intriguing 2.6σ deviation from the Standard Model (SM) prediction. In view of this, we study model independent New Physics (NP) explanations of R K consistent with other ...