Bounds on second generation scalar leptoquarks from the anomalous magnetic moment of the muon

Correlating h→μ^{+}μ^{-} to the Anomalous Magnetic Moment of the Muon via Leptoquarks

Recently, both ATLAS and CMS measured the decay h→μ^{+}μ^{-}, finding a signal strength with respect to the standard model expectation of 1.2±0.6 and 1.19_{-0.39-0.16}^{+0.41+0.17}, respectively. This provides, for the first time, evidence that the standard model Higgs couples to second generation fermions. This measurement is particularly interesting in the context of the intriguing hints for lepton flavor universality violation, accumulated within recent years, as new physics explanations could also be tested in the h→μ^{+}μ^{-} decay mode. Leptoquarks are prime candidates to account for the flavor anomalies. In particular, they can provide the necessary chiral enhancement (by a factor m_{t}/m_{μ}) to address a_{μ} with tera-electron-volt scale new physics. In this Letter we point out that such explanations of a_{μ} also lead to enhanced effects in h→μ^{+}μ^{-} and we examine the correlations between h→μ^{+}μ^{-} and a_{μ} within leptoquark models. We find that the effect in the branching ratio of h→μ^{+}μ^{-} ranges from several percent up to a factor of 3, if one aims at accounting for a_{μ} at the 2σ level. Hence, the new ATLAS and CMS Collaboration measurements already provide important constraints on the parameter space, rule out specific a_{μ} explanations, and will be very important to test the flavor anomalies in the future.

Leptoquarks in Flavour Physics

While the LHC has not directly observed any new particle so far, experimental results from LHCb, BELLE and BABAR point towards the violation of lepton flavour universality in b ⟶ sℓ+ and b ⟶ c-ℓν. In this context, also the discrepancy in the anomalous magnetic moment of the muon can be interpreted as a sign of lepton flavour universality violation. Here we discuss how these hints for new physics can also be explained by introducing leptoquarks as an extension of the Standard Model. Indeed, leptoquarks are good candidates to explain the anomaly in the anomalous magnetic moment of the muon because of an mg/mμ enhanced contribution giving correlated effects in Z boson decays which is particularly interesting in the light of future precision experiments.