Probing scalar and pseudoscalar new physics using rare kaon decays

TL;DR

This paper investigates how rare kaon decays can reveal new scalar and pseudoscalar physics effects, emphasizing the importance of various decay modes and upcoming experiments for comprehensive testing.

Contribution

It provides a detailed analysis of scalar and pseudoscalar operators in rare kaon decays, highlighting the complementary roles of different decay modes and experimental setups.

Findings

Forward-backward asymmetry in $K^+ o o u$ decays as a clean scalar probe

Stringent constraints from $K_L o u$ decays

Future measurements of $K_S o u$ and $K_L o o u$ can discover new physics

Abstract

Rare kaon decays provide sensitive tests of new physics. In this work, we focus on scalar and pseudoscalar operators, analysing the $K\to \pi \ell^+\ell^-$ and $K\to \ell^+\ell^-$ decays. We highlight the complementary role of different modes: $K^+\to\pi^+\ell^+\ell^-$, in particular the forward-backward asymmetry in the muon channel as a clean probe of scalar effects, the stringent constraints from $K_L\to \mu^+\mu^-$, and the discovery potential of future measurements of $K_S\to \mu^+\mu^-$ and $K_L\to \pi^0 \ell^+\ell^-$. The interplay between charged and neutral modes underscores the complementarity of NA62, the LHCb upgrade, and KOTO-II.