Correlating $h\toμ^+μ^-$ to the Anomalous Magnetic Moment of the Muon via Leptoquarks

Abstract: Recently, both ATLAS and CMS measured the decay $h\to\mu^+\mu^-$, finding a signal strength with respect to the Standard Model expectation of $1.2\pm0.6$ and $1.19\substack{+0.41+0.17\-0.39 -0.16}$, 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 $h\to\mu^{+}\mu^{-}$ decay mode. Leptoquarks are prime candidates to account for the flavor anomalies. In particular, they can provide the necessary chiral enhancement (by a factor $m_t/m_\mu$) to address $a_\mu$ with TeV scale new physics. In this letter we point out that such explanations of $a_\mu$ also lead to enhanced effects in $h\to\mu^+\mu^-$ and we examine the correlations between $h\to\mu^+\mu^-$ and $a_\mu$ within leptoquark models. We find that the effect in the branching ratio of $h\to\mu^+\mu^-$ ranges from several percent up to a factor three, if one aims at accounting for $a_\mu$ at the $2\,\sigma$ level. Hence, the new ATLAS and CMS measurements already provide important constraints on the parameter space, rule out specific $a_\mu$ explanations and will be very important to test the flavor anomalies in the future.