WG3 Summary -- Rare $B$, $D$ and $K$ decays

TL;DR

This paper summarizes recent experimental and theoretical developments in rare $B$, $D$, and $K$ decays, highlighting constraints on CKM matrix elements and current discrepancies in semi-leptonic $B$ decays.

Contribution

It provides a comprehensive overview of the latest results and discussions from the CKM2021 working group on rare meson decays, including experimental constraints and anomalies.

Findings

Constraints on $V_{td}/V_{ts}$ and $ ext{epsilon}^ ext{'}/ ext{epsilon}$ updated

Discrepancies in semi-leptonic $B$ decays highlighted

Summary of experimental and theoretical progress in rare decays

Abstract

We summarize the presentations made within Working Group 3 of the CKM2021 workshop. This working group is devoted to rare $B$, $D$ and $K$ decays, radiative and electroweak-penguin decays, including constraints on $V_{\rm td}/V_{\rm ts}$ and $\epsilon^\prime / \epsilon$. The working group has thus a very broad scope, and includes very topical subjects such as the coherent array of discrepancies in semi-leptonic $B$ decays. Each contribution is here summarized very succinctly with the aim of providing an overview of the main results. The reader interested in fuller details is referred to the individual contributions.