Muon $g-2$ and scalar leptoquark mixing

Abstract

The observed muon anomalous magnetic moment deviates from the Standard Model predictions. There are two scalar leptoquarks with simultaneous couplings to the quark-muon pairs of both chiralities that can singly explain this discrepancy. We discuss an alternative mechanism that calls for the mixing of two scalar leptoquarks of the same electric charge through the interaction with the Higgs field, where the two leptoquarks separately couple to the quark-muon pairs of opposite chirality structures. Three scenarios that satisfy this requirement are $S_1\,\&\, {S}_3$, $\widetilde{S}_1\,\&\, S_3$, and $\widetilde{R}_2\,\&\, R_2$, where the first scenario is realised with the up-type quarks running in the loops while the other two scenarios proceed through the down-type quark loops. We introduce only two non-zero Yukawa couplings to the relevant quarks and a muon, at the time, to study ability of these three scenarios to explain $(g-2)_\mu$ and be in accord with available experimental constraints. We find that the $S_1\,\&\, {S}_3$ scenario with the top-quark loops is consistent with all existing measurements. The $\widetilde{S}_1\,\&\, S_3$ and $\widetilde{R}_2\,\&\, R_2$ scenarios can accommodate the observed discrepancy through the bottom-quark loops but exhibit significant tension with the existing data on the high-$p_T$ dilepton-tails at LHC for the required values of Yukawa couplings and leptoquark masses.