Implications of $$B \rightarrow K \nu {\bar{\nu }}$$ B → K ν ν ¯ under rank-one flavor violation hypothesis

Abstract

Abstract We study the implications of the observed excess in $$B^+ \rightarrow K^+ \nu \bar{\nu }$$ B + → K + ν ν ¯ under the assumption of Rank-One Flavour Violation, i.e. that New Physics couples to a single specific direction in flavour space. By varying this direction we perform analyses at the level of the low-energy EFT, the SMEFT, and with explicit mediators such as leptoquarks and colorless vectors ( $$Z^\prime $$ Z ′ and $$V^\prime $$ V ′ ). We study correlations with other flavour, electroweak and collider observables, finding that the most interesting ones are with $$K \rightarrow \pi \nu \bar{\nu }$$ K → π ν ν ¯ , $$B_s \rightarrow \mu ^+ \mu ^-$$ B s → μ + μ - , meson mixing and the LHC searches in $$\tau ^+ \tau ^-$$ τ + τ - high-energy tails. Among the various mediators, the scalar leptoquarks $$\tilde{R}_2$$ R ~ 2 and $$S_1$$ S 1 offer the best fits of the Belle-II excess, while being consistent with the other bounds. On the other hand, colorless vectors are strongly constrained by meson mixing and resonance searches in $$p p \rightarrow \tau ^+ \tau ^-$$ p p → τ + τ - . In all cases we find that a flavour alignment close to the third generation is generically preferred.