Right-handed Neutrinos in Semileptonic B Decays
The observed ratios of semitauonic versus light semileptonic B to charm decays -- denoted R(D) or R(D*) -- exhibit a tension at approximately the 4 sigma level compared to theoretically clean Standard Model (SM) predictions. This persistent anomaly is observed at three different experiments in various exclusive modes. We'll discuss the case that the semitauonic decay involves a sterile, right-handed neutrino, rather than a left-handed SM one. This discussion will include an EFT analysis of the space of possible simplified models, as well as relevant flavor, collider and cosmological bounds. Along the way, we'll also discuss various caveats and pitfalls in developing theory explanations of the R(D, D*) anomalies, and useful flavor model-building mechanisms.
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