Maximal flavour violation: a Cabibbo mechanism for leptoquarks

Luca Di Luzio,Marco Nardecchia,Javier Fuentes-Martin,Sophie Renner,Admir Greljo

doi:10.1007/jhep11(2018)081

Abstract

We propose a mechanism that allows for sizeable flavour violation in quark-lepton currents, while suppressing flavour changing neutral currents in quark-quark and lepton-lepton sectors. The mechanism is applied to the recently proposed “4321” renormalizable model, which can accommodate the current experimental anomalies in B-meson decays, both in charged and neutral currents, while remaining consistent with all other indirect flavour and electroweak precision measurements and direct searches at high-pT. To support this claim, we present an exhaustive phenomenological survey of this fully calculable UV complete model and highlight the rich complementarity between indirect and direct searches.

Highlights

In the recent years the central question of flavour physics beyond the Standard Model (SM) has been the following: “How is it possible to reconcile TeV-scale new physics (NP) with the absence of indirect signals in flavour changing neutral currents (FCNC)?”
We propose a mechanism that allows for sizeable flavour violation in quarklepton currents, while suppressing flavour changing neutral currents in quark-quark and lepton-lepton sectors
The difficulties in constructing a viable and coherent NP interpretation of the flavour anomalies are due to the simultaneous presence of the following aspects of the phenomenological situation: 1. the NP contribution in b → cτ ν needs to be very large, since it must compete with a SM tree-level process; 2. there is an absence of NP signals in direct searches at the LHC; 3. there are very severe constraints from flavour observables in pure hadronic channels, most notably in ∆F = 2 transitions; 4. there are very severe constraints from flavour observables in pure leptonic channels, most notably in processes violating lepton universality and lepton flavour

Summary

Introduction

In the recent years the central question of flavour physics beyond the Standard Model (SM) has been the following: “How is it possible to reconcile TeV-scale new physics (NP) (as suggested e.g. by naturalness) with the absence of indirect signals in flavour changing neutral currents (FCNC)?”. A coherent pattern of SM deviations in semileptonic B-decays, which goes under the widely accepted name of “flavour anomalies”, keeps building up since 2012 [2,3,4,5,6,7,8,9,10,11,12,13]. Were these anomalies due to NP, they would certainly imply a shift of paradigm in flavour physics.

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Conclusion