# Rare B, D and K decays, radiative and electroweak penguin decays, including constraints on $V_{td}/V_{ts}$ and $\epsilon'/\epsilon$: Summary of CKM 2018 working group 3

## TL;DR

This paper reviews rare decays of B, D, and K mesons as probes for testing the Standard Model and constraining New Physics, emphasizing experimental challenges and the importance of precise QCD understanding.

## Contribution

It summarizes the status and potential of rare meson decays in testing the Standard Model and constraining New Physics, including recent experimental and theoretical developments.

## Key findings

- Rare decays are sensitive probes of New Physics.
- Precise QCD knowledge is crucial for interpreting decay measurements.
- Correlated deviations in different decays can indicate New Physics.

## Abstract

Rare $B$, $D$ and $K$ decays provide interesting probes of the Standard Model (SM), with a potential sensitivity to New Physics (NP) higher than other, more common, decays. Their experimental measurement is challenging, and their theoretical interpretation requires a precise knowledge of QCD at low energies, in the non-perturbative (hadronic) regime. The various $b$, $c$, $s$ decays provide different types of tests of the Standard Model, which can be performed in different experimental settings and which may exhibit correlated deviations in models of New Physics.