Kaon Portal to Freeze-in Dark Matter

TL;DR

This paper explores how light dark matter produced via kaon decays in a low-reheating universe can be tested through rare kaon decay experiments, linking cosmology and particle physics.

Contribution

It introduces a novel mechanism for freeze-in dark matter production via quark flavor-changing operators in low-reheating cosmology, connecting it to experimental searches.

Findings

Lower reheating temperatures increase the required coupling strength.

Kaon decays can produce the observed dark matter abundance.

Rare kaon decay experiments can test this dark matter production mechanism.

Abstract

We investigate freeze-in production of light dark matter through the quark flavor-changing operator $(\bar{s}\gamma_\mu d)(\bar{\chi}\gamma^\mu\chi)$ in a low-reheating cosmology. For reheating temperatures below the QCD crossover, kaon decays and scatterings generate the dark matter abundance through $K\to\pi\chi\bar{\chi}$ and $K\pi\to\chi\bar{\chi}$. The same interaction induces the rare kaon decays $K^+\to\pi^+\chi\bar{\chi}$ and $K_L\to\pi^0\chi\bar{\chi}$. This links the freeze-in relic abundance to searches at NA62, KOTO, and KOTO II. We find that lower reheating temperatures require larger couplings to compensate for the Boltzmann-suppressed kaon abundance, making kaon-driven freeze-in dark matter testable at rare kaon decay experiments.