Light Scalars and the KOTO Anomaly

Phys.Rev.Lett124 (2019), no. 19, 191801

In this letter, we investigate potential new physics explanations of the recently observed excess of events at the KOTO experiment, which is searching for a rare decay of the Kaon. We examine two new physics scenarios: the minimal extension of the Standard Model with a new scalar that mixes with the SM Higgs (the so-called “Higgs Portal”), and a “hadrophilic scalar mediator”, which couples only to the up-type quarks. We find that both models can explain the observed events, avoiding all current constraints in two different ways, which provides strong motivation for new physics explanations of the events at KOTO.