Neutrino magnetic moment in the doublet-singlet Leptoquark model

Abstract

The transition magnetic moment for Majorana neutrinos is studied in a simple extension of the Standard Model. This extension incorporates two scalar Leptoquarks $S_1$ and $\widetilde{R}_2$ with quantum numbers $(\bar{3},1,1/3)$ and $(3,2,1/6)$ respectively. It is found that these Leptoquarks generate a sizable transition magnetic moment, particularly when the quark bottom is running in the loop. For our analysis of the parameter space, we include the latest measurement of the muon magnetic moment and combine it with the experimental constraint on the branching ratio Br$(τ\to μγ)$. We found that, despite the recent agreement on the $(g-2)_μ$ value, large values for Leptoquark Yukawa couplings are allowed due to a degeneracy in the parameters. Additionally, we explore how the Leptoquark model addresses the anomalies observed in the ratios of semileptonic $B$ meson decays, $R_{D^{(*)}}$. We determine that the restrictions derived from our analysis are consistent with the most recent experimental limits reported by the XENONnT and LUX-ZEPLIN collaborations. This conclusion is based on our evaluation of the transition magnetic moment from muon neutrino to tau neutrino, focusing on the allowed region for the Leptoquark Yukawa couplings.