New physics searches at kaon and hyperon factories.

Rare meson decays are among the most sensitive probes of both heavy and light new physics. Among them, new physics searches using kaons benefit from their small total decay widths and the availability of very large datasets. On the other hand, useful complementary information is provided by hyperon decay measurements. We summarize the relevant phenomenological models and the status of the searches in a comprehensive list of kaon and hyperon decay channels. We identify new search strategies for under-explored signatures, and demonstrate that the improved sensitivities from current and next-generation experiments could lead to a qualitative leap in the exploration of light dark sectors.

Lepton flavor violation in B decays?

The LHCb Collaboration's measurement of R_{K}=B(B^{+}→K^{+}µ^{+}µ^{-})/B(B^{+}→K^{+}e^{+}e^{-}) lies 2.6σ below the Standard Model prediction. Several groups suggest this deficit to result from new lepton nonuniversal interactions of muons. But nonuniversal leptonic interactions imply lepton flavor violation in B decays at rates much larger than are expected in the Standard Model. A simple model shows that these rates could lie just below current limits. An interesting consequence of our model, that B(B_{s}→µ^{+}µ^{-})_{exp}/B(B_{s}→µ^{+}µ^{-})_{SM}≅R_{K}≅0.75, is compatible with recent measurements of these rates. We stress the importance of searches for lepton flavor violations, especially for B→Kµe, Kµτ, and B_{s}→µe, µτ.