B-decay anomalies in a composite leptoquark model

Abstract

The collection of a few anomalies in semileptonic B-decays, especially in b → cτν, invites to speculate about the emergence of some striking new phenomena, perhaps interpretable in terms of a weakly broken U (2) n flavor symmetry and of leptoquark mediators. Here we aim at a partial UV completion of this interpretation by generalizing the minimal composite Higgs model to include a composite vector leptoquark as well.

On the importance of electroweak corrections for B anomalies

“…4 Such requirement is an output of our analysis and represents a necessary condition to simultaneously accommodate the anomalies in B → Kµ + µ − 3 In principle, such a conclusion could be invalidated by large cancellations among different NP contributions entering R τ / τ with a required fine-tuning of order 10% [80,81]. So far, no UV-complete model accomplishing this task appeared in the literature.…”

“…Moreover, there are four types of lepto-quark (LQ) mediators giving rise to O (1) lq and O (3) lq at the tree-level [80,[94][95][96][97][98][99][100][101]. Two have spin one, U µ and U a µ , and two have spin zero, S and S a .…”

“…Z or leptoquarks, rely on a U(2) flavour breaking pattern [80,81,97]. Common feature of models with U(2) flavour symmetries is the existence of small flavour symmetry breaking parameters which suppress the coupling of NP with the first two fermion generations.…”

“…In the case of a color-singlet mediator we can easily see that, after suitable rescaling, Q and L take the form [80,81,97]:…”

Flavour anomalies after the R K ∗ measurement

“…Models featuring vector LQs models in order to explain the flavour anomalies appeared recently in the literature [72][73][74][75], typically as new composite states. The presence of these states signals that the theory in isolation is non-renormalizable, meaning that loop effects of the vectors are UV divergent, for a recent re-discussion see ref.…”