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<p>We analyze the three-body decays of the long-lived neutral kaon <i>K</i><sub><i>L</i></sub> → <i>ππa</i>, where <i>a</i> is an axion-like particle (ALP), and compare them to the two-body decay <i>K</i><sub><i>L</i></sub> → <i>π</i><sup>0</sup><i>a</i>. While the latter requires both flavor violation (FV) and <i>CP</i> violation (CPV), the former can proceed via FV alone, allowing the ratio of decay rates to serve as a probe of CPV of the underlying UV theory. We emphasize the importance of weak-interaction-induced contributions, often neglected in recent calculations. We explore both minimal and non-minimal flavor-violating scenarios, and identify classes of models where ALP production from neutral three-body decays is comparable to — or even dominates over — the two-body decay, despite its reduced phase space. Finally, we discuss the phenomenological implications of our results and show how these decays can provide complementary probes of ALP couplings beyond those accessible via charged kaon channels.</p>

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Probing CP and flavor violation in neutral kaon decays with ALPs

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年2月2日

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  • Reuven Balkin,
  • Stefania Gori,
  • Christiane Scherb

摘要

We analyze the three-body decays of the long-lived neutral kaon KL → ππa, where a is an axion-like particle (ALP), and compare them to the two-body decay KL → π0a. While the latter requires both flavor violation (FV) and CP violation (CPV), the former can proceed via FV alone, allowing the ratio of decay rates to serve as a probe of CPV of the underlying UV theory. We emphasize the importance of weak-interaction-induced contributions, often neglected in recent calculations. We explore both minimal and non-minimal flavor-violating scenarios, and identify classes of models where ALP production from neutral three-body decays is comparable to — or even dominates over — the two-body decay, despite its reduced phase space. Finally, we discuss the phenomenological implications of our results and show how these decays can provide complementary probes of ALP couplings beyond those accessible via charged kaon channels.