Vector leptoquarks beyond tree level. III. Vectorlike fermions and flavor-changing transitions

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When a TeV-scale leptoquark has a sizeable Yukawa coupling, its dominant production mechanism at hadron colliders is the partonic-level lepton-quark fusion. Even though the parton distribution functions for leptons inside the proton are minuscule, they get compensated by the resonant enhancement. We present the first computation of higher order radiative corrections to the resonant leptoquark production cross section at the Large Hadron Collider (LHC). Next-to-leading (NLO) QCD and QED corrections are similar in size but come with the opposite sign. We compute NLO K-factors for a wide range of scalar leptoquark masses, as well as, all possible combinations of quark and lepton flavors and leptoquark charges. Theoretical uncertainties due to the renormalisation and factorisation scale variations and the limited knowledge of parton distribution functions are quantified. We finally discuss how to disentangle the flavor structure of leptoquark interactions by exploiting the interplay between different production channels.

Section: Introductionmentioning

confidence: 95%

Lepton-quark fusion at Hadron colliders, precisely

Greljo

Selimovic

2021

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Section: Llmentioning

confidence: 99%

“…For instance, in the class of models analyzed in [59,91], in which the U 1 leptoquark is a massive gauge boson, the scale Λ bs relevant to B s -B s mixing is related to the mass M L of the vector-like leptons, which are responsible for the 2-3 flavor mixing in the U 1 couplings. More precisely, for M L M U one finds that Λ bs ≈ M L [59]. The fact that in these models Λ bs is associated with the mass of a colorless particle (a vector-like lepton) is a highly non-trivial feature, which allows for a relatively low value Λ bs 1 TeV without conflicting with current bounds from direct searches at the LHC (see section 4 for more details).…”

Section: Llmentioning

confidence: 99%

“…However, as we shall discuss, many of the phenomenological conclusions we can derive from the present data are valid for the wider class of models where the U 1 is the main mediator of the anomalies, including in particular the well motivated case of models of compositeness. The gauge-theory extension offers the advantage of allowing for a systematic estimate of quantum corrections [57][58][59]. We will thus refer specifically to this option when discussing UV-sensitive observables.…”

Section: Introductionmentioning

confidence: 99%

“…• The analysis in section 4 takes into account, for the first time, complete NLO corrections in the leptoquark coupling α 4 , which were computed in [57][58][59] within the non-universal 4321 model. The latter play a key role in the predictions we obtain for B-meson mixing and the rare decay B → Kνν.…”

Section: Introductionmentioning

confidence: 99%

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Reading the footprints of the B-meson flavor anomalies

Cornella

Faroughy

Fuentes-Martín

et al. 2021

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125

128

Motivated by the recent LHCb announcement of a 3.1σ violation of lepton- flavor universality in the ratio RK = Γ(B → Kμ+μ−)/Γ(B → Ke+e−), we present an updated, comprehensive analysis of the flavor anomalies seen in both neutral-current (b → sℓ+ℓ−) and charged-current (b → $$ c\tau \overline{\nu} $$ cτ ν ¯ ) decays of B mesons. Our study starts from a model-independent effective field-theory approach and then considers both a simplified model and a UV-complete extension of the Standard Model featuring a vector leptoquark U1 as the main mediator of the anomalies. We show that the new LHCb data corroborate the emerging pattern of a new, predominantly left-handed, semileptonic current-current interaction with a flavor structure respecting a (minimally) broken U(2)5 flavor symmetry. New aspects of our analysis include a combined analysis of the semileptonic operators involving tau leptons, including in particular the important constraint from Bs-$$ {\overline{B}}_s $$ B ¯ s mixing, a systematic study of the effects of right-handed leptoquark couplings and of deviations from minimal flavor-symmetry breaking, a detailed analysis of various rare B-decay modes which would provide smoking-gun signatures of this non-standard framework (LFV decays, di-tau modes, and B → K(*)$$ \nu \overline{\nu} $$ ν ν ¯ ), and finally an updated analysis of collider bounds on the leptoquark mass and couplings.

Low-energy phenomenology of scalar leptoquarks at one-loop accuracy

Gherardi

Marzocca

Venturini

2021

103

We perform a complete study of the low-energy phenomenology of S1 and S3 leptoquarks, aimed at addressing the observed deviations in B-meson decays and the muon magnetic dipole moment. Leptoquark contributions to observables are computed at one-loop accuracy in an effective field theory approach, using the recently published complete one-loop matching of these leptoquarks to the Standard Model effective field theory. We present several scenarios, discussing in each case the preferred parameter space and the most relevant observables.