$K\to\mu^+\mu^-$ beyond the standard model

TL;DR

This paper explores how new physics could significantly enhance the rare decay rate of $K_S$ to muons, using a novel interference measurement method, providing a promising avenue for detecting physics beyond the Standard Model in kaon decays.

Contribution

It introduces a new method to measure CP-violating decay rates in kaons and analyzes its sensitivity to new physics both model-independently and within specific scenarios.

Findings

Simple NP models can greatly increase the decay rate of $K_S\to\mu^+\mu^-$

The proposed method offers a promising probe for physics beyond the Standard Model

The decay rate is related to other observables like $K_L\to\pi^0\nu\bar\nu$

Abstract

We analyze the New Physics sensitivity of a recently proposed method to measure the CP-violating ${\cal B}(K_S\to\mu^+\mu^-)_{\ell=0}$ decay rate using $K_S - K_L$ interference. We present our findings both in a model-independent EFT approach as well as within several simple NP scenarios. We discuss the relation with associated observables, most notably ${\cal B}(K_L\to\pi^0\nu\bar\nu)$. We find that simple NP models can significantly enhance ${\cal B}(K_S\to\mu^+\mu^-)_{\ell=0}$, making this mode a very promising probe of physics beyond the standard model in the kaon sector.