Discriminating Tauphilic Leptoquark Explanations of the $B$ Anomalies via $K\to \pi\nu\bar\nu$ and $B\to K\nu\bar\nu$

TL;DR

This paper investigates how specific leptoquark models can explain B decay anomalies and affect neutrino-related decay modes, providing constraints and identifying which models can produce observable effects consistent with current experimental data.

Contribution

It analyzes two minimal leptoquark models to determine their effects on neutrino modes and their compatibility with B decay anomalies and experimental limits.

Findings

Large effects in B→K(*)νν̄ are only possible in the S1+S3 model.

Both models can explain the K+→π+νν̄ central value.

Neutrino channels impose significant constraints on leptoquark parameter space.

Abstract

Leptoquark models are prime candidates for new physics (NP) explanations of the long-standing anomalies in semi-leptonic $B$ decays; $b\to c \tau \bar\nu$ (encoded in $R(D^{(\ast)})$) and $b\to s\ell\bar\ell (\ell=e,\mu)$ transitions. Furthermore, Belle II and NA62 reported weaker-than-expected limits on $B^+ \to K^+ \nu\bar\nu$ and $K^+ \to \pi^+ \nu \bar\nu$, respectively. While the $R(D^{(\ast)})$ and $b\to s\ell \bar\ell$ measurements can be explained with NP contributions at the $O(10\%)$ level, the neutrino channels suggest that the NP effect could be comparable in size to the Standard Model one. In this context, we consider the two types of leptoquark models with minimal sets of the couplings that can best describe the semi-leptonic $B$ anomalies and lead at the same time to effects in the neutrino modes, the singlet-triplet scalar leptoquark model ($S_1+S_3$) and the singlet vector leptoquark model ($U_1$). More specifically, the neutrino channels pose non-trivial constraints on the parameter space, and we find that large effects (i.e., accounting for the current central value) in $B\to K^{(*)}\nu\bar\nu$ are only possible in the $S_1+S_3$ setup, while both models can account for the central value of $K^+\to \pi^+\nu\bar\nu$.