Abstract
Experimental measurements of the ratios Rleft({D}^{left(ast right)}right)equiv frac{Gamma left(Bto {D}^{left(*right)}tau vright)}{Gamma left(Bto {D}^{left(*right)}ell vright)}left(ell =e,mu right) show a 3.9σ deviation from the Standard Model prediction. In the absence of light right-handed neutrinos, a new physics contribution to b → cτν decays necessarily modifies also boverline{b}to {tau}^{+}{tau}^{-} and/or coverline{c}to {tau}^{+}{tau}^{-} transitions. These contributions lead to violation of lepton flavor universality in, respectively, Y and ψ leptonic decays. We analyze the constraints resulting from measurements of the leptonic vector-meson decays on solutions to the R(D(*)) puzzle. Available data from BaBar and Belle can already disfavor some of the new physics explanations of this anomaly. Further discrimination can be made by measuring Y(1S, 2S, 3S) → ττ in the upcoming Belle II experiment.
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