Leptoquarks meet ε′/ε and rare Kaon processes

Abstract

We analyse for the first time the CP violating ratio ε /ε in K → ππ decays in leptoquark (LQ) models. Assuming a mass gap to the electroweak (EW) scale, the main mechanism for LQs to contribute to ε /ε is EW gauge-mixing of semi-leptonic into nonleptonic operators, which we treat in the Standard Model effective theory (SMEFT). We perform also the one-loop decoupling for scalar LQs, finding that in all models with both left-handed and right-handed LQ couplings box-diagrams generate numerically strongly enhanced EW-penguin operators Q 8,8 already at the LQ scale. We then investigate correlations of ε /ε with rare Kaon processes (K L → π 0 νν, K + → π + νν, K L → π 0 ¯ , K S → µμ, ∆M K and ε K ) and find that even imposing only a moderate enhancement of (ε /ε) NP = 5 × 10 −4 to explain the current anomaly hinted by the Dual QCD approach and RBC-UKQCD lattice QCD calculations leads to conflicts with experimental upper bounds on rare Kaon processes. They exclude all LQ models with only a single coupling as an explanation of the ε /ε anomaly and put strong-to-serious constraints on parameter spaces of the remaining models. Future results on K + → π + νν from the NA62 collaboration, K L → π 0 νν from the KOTO experiment and K S → µμ from LHCb will even stronger exhibit the difficulty of LQ models in explaining the measured ε /ε, in case the ε /ε anomaly will be confirmed by improved lattice QCD calculations. Hopefully also improved measurements of K L → π 0 ¯ decays will one day help in this context.

Flavor-changing hyperon decays with light invisible bosons

“…Among their kaon counterparts, the data on K → π / E are the closest to their SM expectations. Particularly, the E949 [2] and KOTO [4] findings, B(K + → π + νν) = 1.7(1.1) × 10 −10 [5] and B K L → π 0 νν < 3.0 × 10 −9 at 90% confidence level (CL), respectively, are not far from the SM numbers B(K + → π + νν) = 8.5 +1.0 −1.2 × 10 −11 and B(K L → π 0 νν) = 3.2 +1.1 −0.7 × 10 −11 [26]. We can regard the upper ends of the 90%-CL ranges of their deviations from the SM predictions,…”

Lepton-flavor-violating semileptonic τ decay and K→πνν¯

“…(21)- (22). In view of the SM predictions B(K + → π + νν) = 8.5 +1.0 −1.2 × 10 −11 and B(K L → π 0 νν) = 3.2 +1.1 −0.7 × 10 −11 [39] and the data B(K + → π + νν) = 1.7(1.1) × 10 −10 [33] and B K L → π 0 νν < 3.0 × 10 −9 at 90% CL [40], we impose ∆B K + < 2.7 × 10 −10 and ∆B K L < 3.0 × 10 −9 at 90% CL on the NP contributions in Eq. (21).…”

Prospects for measurements with strange hadrons at LHCb

“…, when compared with the current experimental upper limit [3] B(K 0 S → µ + µ − ) < 8 × 10 −10 at 90% CL , leaves room for small BSM contributions to interfere and compete with the SM rate. This is shown to be the case in leptoquark (LQ) models [31,32] as well as in the Minimal Supersymmetric Standard Model (MSSM) [33]. In the LQ case, the enhancements can reach as high as the current experimental bound, while within the MSSM, B(K 0 S → µ + µ − ) can adopt values anywhere in the range [0.…”