Open Access

Discriminating tauphilic leptoquark explanations of the $B$ anomalies via $K \to π ν \bar{ν}$ and $B \to K ν \bar{ν}$

Andreas Crivellin ^1,*, Syuhei Iguro ^2,3,4,†, and Teppei Kitahara ^5,3,‡

¹Physik-Institut, Universität Zürich, Winterthurerstrasse 190, CH–8057 Zürich, Switzerland
²Institute for Advanced Research, Nagoya University, Nagoya 464-8601, Japan
³Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University, Nagoya 464-8602, Japan
⁴KEK Theory Center, IPNS, KEK, Tsukuba 305-0801, Japan
⁵Department of Physics, Graduate School of Science, Chiba University, Chiba 263-8522, Japan

^*Contact author: andreas.crivellin@cern.ch
^†Contact author: igurosyuhei@gmail.com
^‡Contact author: kitahara@chiba-u.jp

Phys. Rev. D 112, 095016 – Published 13 November, 2025

DOI: https://doi.org/10.1103/4dpx-h5vm

Abstract

Leptoquark models are prime candidates for new physics (NP) explanations of the longstanding anomalies in semileptonic $B$ decays; $b \to c τ \bar{ν}$ [encoded in $R (D^{(*)})$ ] and $b \to s ℓ \bar{ℓ} (ℓ = e, μ)$ transitions. Furthermore, Belle II and NA62 reported weaker-than-expected limits on $B^{+} \to K^{+} ν \bar{ν}$ and $K^{+} \to π^{+} ν \bar{ν}$ , respectively. While the $R (D^{(*)})$ and $b \to s ℓ \bar{ℓ}$ 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 semileptonic $B$ 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 nontrivial constraints on the parameter space, and we find that large effects (i.e., accounting for the current central value) in $B \to K^{(*)} ν \bar{ν}$ are only possible in the $S_{1} + S_{3}$ setup, while both models can account for the central value of $K^{+} \to π^{+} ν \bar{ν}$ .

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Phys. Rev. D 112, 095016– Published 13 November, 2025

Vol. 112, Iss. 9 — 1 November 2025

Received 1 September 2025
Accepted 23 October 2025

DOI: https://doi.org/10.1103/4dpx-h5vm

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

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Discriminating tauphilic leptoquark explanations of the $B$ anomalies via $K \to π ν \bar{ν}$ and $B \to K ν \bar{ν}$

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Discriminating tauphilic leptoquark explanations of the B anomalies via K→πνν¯ and B→Kνν¯

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Discriminating tauphilic leptoquark explanations of the $B$ anomalies via $K \to π ν \bar{ν}$ and $B \to K ν \bar{ν}$