The KOTO experiment recently reported four candidate events in the signal region of K_L \to \pi^0 \nu \bar{\nu} search, where the standard model only expects 0.10±0.02 events. If confirmed,  this requires physics beyond the standard model to enhance the signal. In this talk, I will introduce various new physics interpretations of the result including these: (1) heavy new physics boosting the standard model signal, (2) reinterpretation of "\nu \bar{\nu}" as a new light long-lived particle, or (3) reinterpretation of the whole signal as the production of a new light long-lived particle at the fixed target. We study the above explanations in the context of a generalized new physics Grossman-Nir bound coming from the K^+ \to \pi^+ \nu \bar{\nu}decay, bounded by data from the E949 and the NA62 experiments.

I received a Ph.D. in Theoretical Physics from the University of Tokyo in March 2015, where my adviser was Prof. Takeo Moroi. I have experience of postdocs at three places: KEK, Japan, Karlsruhe Institute of Technology, Germany, and Technion, Israel. Now, I belong to Nagoya University as a designated assistant professor.