Searching for New Physics with b → sτ⁺τ^-

In recent years, intriguing hints for the violation of lepton flavor universality (LFU) have been accumulated in semileptonic B decays, both in the charged-current transitions b → cl^-ν^-_l (i.e., R_D, R_D∗, and R_J/Ψ and the neutral-current transitions b → sl⁺l^- (i.e., R_K and R_K∗. Hints for LFU violation in R_D(∗) and R_J/Ψ point at large deviations from the standard model (SM) in processes involving tau leptons. Moreover, LHCb has reported deviations from the SM expectations in b → sμ⁺μ^- processes as well as in the ratios R_K and R_K∗, which together point at new physics (NP) affecting muons with a high significance. These hints for NP suggest the possibility of huge LFU-violating effects in b → sτ⁺τ^- transitions. In this Letter, we predict the branching ratios of B → Kτ⁺τ^-, B → K^∗τ⁺τ^-, and B_s → Φτ⁺τ^-, taking into account NP effects in the Wilson coefficients C^ττ_9(') and C^ττ_10('). Assuming a common NP explanation of R_D, R_D(∗), and R_J/Ψ, we show that a very large enhancement of b → sτ⁺τ^- processes, of around 3 orders of magnitude compared to the SM, can be expected under fairly general assumptions. We find that the branching ratios of B_s → τ⁺τ^-, B_s → Φτ⁺τ^-, and B → K^(∗)τ⁺τ^- under these assumptions are in the observable range for LHCb and Belle II.