Flavor Phenomenology of the Leptoquark Singlet-Triplet Model

Abstract

In recent years, experiments revealed intriguing hints for new physics (NP) in semi-leptonic $B$ decays. Both in charged current processes, involving $b\to c\tau \nu$ transitions, and in the neutral currents $b\to s{\ell }^{+}{\ell }^{-}$, a preference for NP compared to the standard model (SM) of more that $3\sigma$ and $5\sigma$ was found, respectively. In addition, there is the long-standing tension between the theory prediction and the measurement of the anomalous magnetic moment (AMM) of the muon ($a_{\mu }$) of more than $3\sigma$. Since all these observables are related to the violation of lepton flavor universality (LFU), a common NP explanation seems not only plausible but is even desirable. In this context, leptoquarks (LQs) are especially promising since they give tree-level effects in semi-leptonic $B$ decays, but only loop-suppressed effects in other flavor observables that agree well with their SM predictions. Furthermore, LQs can lead to a $m_t/m_{\mu }$ enhanced effect in $a_{\mu }$, allowing for an explanation even with (multi) TeV particles. However, a single scalar LQ representation cannot provide a common solution to all three anomalies. In this article we therefore consider a model in which we combine two scalar LQs: the $SU(2{)}_L$ singlet and the $SU(2{)}_L$ triplet. Within this model we compute all relevant one-loop effects and perform a comprehensive phenomenological analysis, pointing out various interesting correlations among the observables. Furthermore, we identify benchmark points which are in fact able to explain all three anomalies ($b\to c\tau \nu$, $b\to s{\ell }^{+}{\ell }^{-}$ and $a_{\mu }$), without violating bounds from other observables, and study their predictions for future measurements.

Comments: 56 pages, 14 figures, 3 tables. Version 3: 57 pages, 15 figures, 4 tables. Updated numerical analysis (added section 4.4.1, Figure 15 and Table 4)