Owing to the strong suppression of flavour-changing neutral-current transitions in the Standard Model, rare kaon decays constitute a superb tool to constrain hypothetical new-physics interactions. At the same time, they provide many interesting tests of the Standard Model itself, being sensitive both to short-distance electroweak scales and to the long-distance QCD dynamics. A brief overview of the current status is presented. The Standard Model prediction for the direct CP-violating ratio $\varepsilon'/\varepsilon$ is also discussed.
The following proceedings contain a theory perspective on rare Kaon decays. I review rare kaon decays in the LHC era: we discuss interplay with B-anomalies and possible New Physics in direct CP violation in $K\to 2π$: very rare kaon decays like $K \to πν\barν$ are very important to this purpose. We discuss also the decays $K^0 \to μ^+ μ^-$ due to the LHCB measurement
I review recent developments in rare and radiative kaon decays from the theory side, with emphasis on those modes that are actively analyzed by the experimental collaborations.
稀有K介子衰变和CP破坏是检验标准模型及其推广的重要工具。我们描述了K介子物理观测值测试CP破坏和更普遍的短距离物理。所考虑的通道将是K -> pi nu nubar、K -> pi 1 + 1-、K+- > pi 3 pi、K+- -> pi+- pi gamma、KS -> mu mu和K+- -> pi+-pi 0 e+ e-。
We explore the possibility of lepton number violation (LNV) manifesting in the rare kaon decay $K\toπνν$, and its consequences for radiative neutrino mass generation and the washout of Lepton asymmetry in high-scale leptogenesis scenarios. We perform the analysis in a model-independent framework, the Standard Model effective field theory (SMEFT), and discuss the possible LNV nature of the rare kaon decay in the context of the currently operating NA62 experiment at CERN. We find that, in case of a LNV interaction, its detection would put high-scale leptogenesis under tension and would hint to s…
We study the $K^0_S-K^0_L$ asymmetries and $CP$ violations in charm-baryon decays with neutral kaons in the final state. The $K^0_S-K^0_L$ asymmetry can be used to search for two-body doubly Cabibbo-suppressed amplitudes of charm-baryon decays, with the one in $Λ^+_c\to pK^0_{S,L}$ as a promising observable. Besides, it is studied for a new $CP$-violation effect in these processes, induced by the interference between the Cabibbo-favored and doubly Cabibbo-suppressed amplitudes with the neutral kaon mixing. Once the new CP-violation effect is determined by experiments, the direct $CP$ asymmetry…
We discuss on the search for the right-handed weak interaction effects in the SU(2)$_L \times$SU(2)$_R$ model with lepton doublets $(ν_\ell, \ell^-)_L$ and $(N_\ell, \ell^-)_R$ ($\ell = e, μ, τ)$. We will point out that only the chance of the observation of the right-handed weak interaction effect will be in the rare decay $K^+ \rightarrow π^- μ^+ μ^+$.
罕见的K介子衰变提供了短距离物理学的灵敏探针。其中最有前途的模式是K+ --> pi+ nu anti-nu和K（L）--> pi 0 nu anti-nu模式，这是由于它们的理论清洁和专用实验，NA 62和KOTO。在这些模式下，新物理学搜索成功的关键是标准模型预测的精度。本文综述了它们的标准模型预测的现状和最新进展，并讨论了K（L）-> pi 0 l+ l-和K（L）-> mu+ mu-衰变的预测和新物理灵敏度。
As measurements of the CKM angle $γ$ in decays of $b$-hadrons become increasingly precise, it is important to consider the impact of processes that affect secondary and tertiary decay products and can contribute to the observed CP violation. The golden decay mode used to measure $γ$ is $B^\pm\to DK^\pm$, where $D\to K_\text{S}^0π^+π^-$. Due to the presence of a $K_\text{S}^0$ meson in the final state, $γ$ measurements based on this mode are affected by neutral kaon CP violation and matter regeneration, and this study examines the potential size of the impact. Previous studies determine the imp…
We investigate the possibility to probe lepton number violating (LNV) operators in the rare kaon decay $K\toπνν$. Performing the analysis in the Standard Model effective field theory with only light active Majorana neutrinos, we determine the current limits on the corresponding LNV physics scale from the past E949 experiment at BNL as well as the currently operating experiments NA62 at CERN and KOTO at J-PARC. We focus on the specific signature of scalar currents in $K\toπνν$ arising from the LNV nature of the operators and study the effect on the experimental sensitivity, stressing the need f…
