Flavour anomalies and the muon $g-2$ from feebly interacting particles

Abstract

We perform a phenomenological analysis of simplified models of light, feebly interacting particles~(FIPs)that can provide a combined explanation of the anomalies in $b\to s{l}^{+}{l}^{-}$ transitions at LHCb and the anomalous magnetic moment of the muon. Different scenarios are categorised according to the explicit momentum dependence of the FIP coupling to the $b-s$ and $\mu -\mu$ vector currents and they are subject to several constraints from flavour and precision physics. We show that viable combined solutions to the muon $g-2$ and flavour anomalies exist with the exchange of a vector FIP with mass larger than $4\text{GeV}$. Interestingly, the LHC has the potential to probe this region of the parameter space by increasing the precision of the $Z\to 4\mu$ cross-section measurement. Conversely, we find that solutions based on the exchange of a lighter vector, in the $m_V<1\text{GeV}$ range, are essentially excluded by a combination of $B\to K+\text{invisible}$ and $W$-decay precision bounds.

Comments: 32 pages, 4 figures. Typos corrected, published version