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Light New Physics in $B\to K^{(*)}\nu\bar\nu$?

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arxiv 2311.14629 v1 pith:AWB5G5JX submitted 2023-11-24 hep-ph hep-ex

classification hep-phhep-ex
keywords belleexcessphysicssigmaanalysisapprox2babardecays
verification ladder T0 review T1 audit T2 compute T3 formal
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abstract

The study of the rare decays $B\to K^{(*)} \nu \bar\nu$ offers a window into the dynamics operating at the electroweak scale, allowing studies of the Standard Model and searches for heavy new physics. However, the analysis of these decays is also potentially sensitive to the on-shell production of new light bosons $X$ through the process $B\to K^{(*)} X$. In particular, Belle~II has recently measured $B^+\to K^+\nu\bar\nu$, finding a $2.8\sigma$ excess under the assumption of heavy new physics. Since this excess is rather localized in the kaon energy, a fit that includes the decay mode $B^+\to K^+ X$ to the kinematic distributions prefers $m_X\approx2\,$GeV with branching fraction Br$[B\to KX]=(8.8\pm2.5)\times 10^{-6}$ and a significance of $\approx3.6\sigma$. However, no excess was found in the BaBar measurements of $B\to K^{(*)} \nu \bar\nu$, and a global analysis of the Belle II and BaBar data leads to Br$[B\to KX]=(5.1\pm2.1)\times 10^{-6}$ with a reduced significance of $\approx2.4\sigma$. We then study various simplified dark-flavoured models and present a possible UV completion based on a gauged $B_3-L_3$ symmetry, highlighting the discovery potential of dedicated searches for $B\to K^{(*)}X$ at Belle II.

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Cited by 5 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. $B\rightarrow K + \text{axion-like particles}$: effective versus UV-complete models and enhanced two-loop contributions

    hep-ph 2025-06 conditional novelty 7.0 of 10

    In the DFSZ axion model, the b to s a transition receives an unsuppressed two-loop contribution proportional to the scalar coupling lambda, which becomes important for tan beta above about 5.

  2. Challenging Majorana neutrino effects in $B\to K^{(\ast)}\nu\nu$ and $K\to \pi\nu\nu$ decays

    hep-ph 2026-07 conditional novelty 6.0 of 10

    Belle-II's B→Kνν excess cannot be explained by dimension-7 lepton-number-violating SMEFT operators without fine-tuning neutrino masses, while a light sterile-neutrino extension can, with testable decay spectra.

  3. A framework for missing-energy searches with anomalous light vectors

    hep-ph 2026-03 conditional novelty 6.0 of 10

    For light U(1)X vectors coupled to anomaly-sensitive currents, Wess-Zumino coefficients are fixed by anomaly matching, which lets all missing-energy searches (K, B, D, Z) be mapped onto one (m_X,g_X) plane with minima...

  4. Radiative generation of chiral vector operators in $b\to s \nu\bar{\nu}$ transition

    hep-ph 2026-01 conditional novelty 6.0 of 10

    Minimal one-loop models that generate both chiral vector operators for b→sνν̄ are systematically classified but cannot quantitatively explain the Belle II anomaly.

  5. A Unified Dark Matter Explanation for $\boldsymbol{B^+ \!\to K^+\nu\bar{\nu}}$ and the Super-Kamiokande Antineutrino Excess

    hep-ph 2026-07 conditional novelty 5.0 of 10

    A UV-complete complex scalar DM model under gauged U(1)Lμ−Lτ accommodates the SK antineutrino excess, the Belle II B+→K+νν̄ excess, and the DM relic density with one light dark sector.

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