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Anomalies and accidental symmetries: charging the scalar leptoquark under L μ − L τ

Published version
Peer-reviewed

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Authors

Kirk, Matthew 
Nardecchia, Marco 

Abstract

Abstract: While the S3 scalar leptoquark presents a possible tree-level explanation of the b → sℓℓ flavour anomalies, it suffers from two conceptual problems which are often disregarded by model-builders. Firstly, the quantum numbers of the S3 allow for a renormalisable diquark operator that would trigger rapid proton decay unless its coupling were tuned away. Secondly, one expects the leptoquark to have generic couplings to leptons, which require tuning to avoid stringent experimental bounds on lepton flavour violation. By gauging a U(1) current that acts as Lμ− Lτ on the Standard Model (SM) fermions, and under which the leptoquark has charge −1, one can remedy both these problems. The additional U(1), which is spontaneously broken at some high scale, is associated with a massive Z′ gauge boson and a scalar SM singlet Φ, which play no direct role in mediating the anomalous B meson decays. By computing one- and two-loop mass corrections, we show that this pair of particles can be hidden away at much higher mass scales without destabilising either the Higgs or the leptoquark masses. The only low-energy relic of gauging Lμ− Lτ is thus the accidental global symmetry structure of the lagrangian. On the other hand, we find quite generally that an S3 leptoquark that mediates the b → sℓℓ anomalies cannot be much heavier than a few TeV without itself inducing large Higgs mass corrections.

Description

Keywords

Regular Article - Theoretical Physics, Beyond Standard Model, Heavy Quark Physics, Global Symmetries

Journal Title

Journal of High Energy Physics

Conference Name

Journal ISSN

1029-8479

Volume Title

2020

Publisher

Springer Berlin Heidelberg