QCD improved matching for semileptonic B decays with leptoquarks

Abstract

Leptoquarks (LQs) provide very promising solutions to the tensions between the experimental measurements and the SM predictions of b → s + − and b → cτ ν processes. In this case the LQ masses are in general at the TeV scale and they can thus be produced at high energy colliders and dedicated LHC searches are ongoing. While for LQ production and decay the O(αs) corrections have been known for a long time, the O(αs) corrections to the matching on 2-quark-2-lepton operators have not been calculated, yet. In this article we close this gap by computing the QCD corrections to the matching of LQ models on the effective SM Lagrangian for both scalar and vector LQs. We find an enhancement of the Wilson coefficients of vector operators with respect to the tree-level results of around 8 % (13 %) if they originate from scalar (vector) LQs. This softens the LHC bounds and increases the allowed parameter space of LQ models addressing the flavour anomalies.

Vector leptoquarks beyond tree level

“…We stress that the effects we have estimated are only due to the new dynamics of the heavy vectors, therefore they should be considered in addition to the QCD corrections to the high-scale matching conditions estimated in [23]. According to this recent analysis, the O(α s ) corrections to C U LL and C U LR go in the same direction of the O(α 4 ) ones, i.e.…”

“…So far, the dynamics of these heavy vectors has been analyzed only at leading order in the leptoquark (LQ) coupling. Next-to-leading order (NLO) effects in QCD have been studied, both at low energies [23] (in the corrections to the coefficients of the corresponding fourfermion operators), and at high energies [22] (in LQ production and decay at colliders). However, NLO corrections associated to the heavy dynamics have never been analyzed.…”

High- $$p_T$$ p T signatures in vector–leptoquark models

“…In our Feynrules implementation and in all our results throughout this paper, we include only tree-level effects. While some NLO QCD corrections are available for the vector leptoquark case [56], in specific models these are expected to be supplemented by additional NLO contributions that can be of similar (or even larger) size. Hence we opt not to include them and we add a systematic error in our signal to (partially) account for them.…”

B-decay discrepancies after Moriond 2019

“…Consequently, for a given leptoquark mass, a τ -channel contribution to R D ( * ) depends only on g 32 lq and g 33 lq , while a µ-channel contribution to R K ( * ) depends only on g 22 lq and g 23 lq . The NLO corrections to such semileptonic operators are known to be of the order 13% [96] and will be neglected in the following.…”