Abstract
In this article we perform a combined analysis of low energy precision constraints and LHC searches for leptoquarks which couple to first generation fermions. Considering all ten leptoquark representations, five scalar and five vector ones, we study at the precision frontier the constraints from $K\to\pi\nu\nu$, $K\to\pi e^+e^-$, $K^0-\bar K^0$ and $D^0-\bar D^0$ mixing, as well as from experiments searching for parity violation (APV and QWEAK). We include LHC searches for $s$-channel single resonant production, pair production and Drell-Yan-like signatures of leptoquarks. Interestingly, we find that the recent non-resonant di-lepton analysis of ATLAS provides stronger bounds than the resonant searches recasted so far to constrain $t$-channel production of leptoquarks. Taking into account all these bounds, we observe that none of the leptoquark representations can address the so-called "Cabibbo angle anomaly" via a direct contribution to super-allowed beta decays.
Highlights
Leptoquarks (LQs) were first proposed in the context of the Pati-Salam model [1] and SUð5Þ grand unified theories [2,3] but later on postulated in composite models with quark and lepton substructure [4], the strong coupling version of the Standard Model (SM) [5], horizontal symmetry theories [6], extended technicolor [7] as well as in SOð10Þ [8], SUð15Þ [9], superstring-inspired E6 models [10] and the R-parity violating minimal supersymmetric Standard Model
We included the constraints from parity violating experiments (Qweak þ atomic parity violation (APV)) and LHC searches, in particular pair production (PP), single resonant production (SRP) and DY searches
We find that the latest nonresonant dilepton analysis of ATLAS provides stronger bounds than resonant searches recasted so far in the literature
Summary
Leptoquarks (LQs) were first proposed in the context of the Pati-Salam model [1] and SUð5Þ grand unified theories [2,3] but later on postulated in composite models with quark and lepton substructure [4], the strong coupling version of the Standard Model (SM) [5], horizontal symmetry theories [6], extended technicolor [7] as well as in SOð10Þ [8], SUð15Þ [9], superstring-inspired E6 models [10] and the R-parity violating minimal supersymmetric Standard Model (see e.g., Ref. [11] for a review). Within recent years LQs experienced a revival, mainly due to the so-called “flavor anomalies.” These are discrepancies between measurements and the SM predictions which point toward lepton flavor universality (LFU) violating new physics (NP) in RðDðÃÞÞ [20,21,22,23,24,25], b → slþl− [26,27,28,29,30,31] and in the anomalous magnetic moment of the muon (aμ) [32], with a significance of >3σ [33,34,35,36,37], >5σ [38,39,40,41,42,43,44,45] and >3σ [46], respectively.
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