A lesson from $R_{\tau \tau }^{K^{(\ast )}}$ and $R_{\nu \nu }^{K^{(\ast )}}$ at Belle II

Abstract

Within the assumption of Left-Handed (LH) New Physics (NP), we review the relations between $\mathcal{B}(B\to K^{(\ast )}{\tau }^{+}{\tau }^{-})$ and $\mathcal{B}(B\to K^{(\ast )}\nu \bar{\nu })$ for several Beyond the Standard Model (BSM) scenarios, commonly considered to explain the Lepton flavor Universality (LFU) violation observed in charged and neutral-current semileptonic $B$ decays. We employ the latest $R_{D^{(\ast )}}$ world averages that include the recent LHCb measurement and assess the possibility of simultaneously explaining the $B$-anomalies without spoiling current bounds on di-neutrino and di-tau modes. This is particularly relevant in light of the upcoming results by Belle II on neutrinos and the continuing improvement in accuracy and sensitivity achieved in tau modes.

Comments: 8 pages, 1 figure