Flavour symmetries in the SMEFT

TL;DR

This paper classifies dimension-six fermionic operators in the SMEFT using $U(3)^5$ and $U(2)^5$ flavour symmetries, aiding the understanding of flavour structures and their implications for high-energy collider analyses.

Contribution

It provides a systematic counting and classification of operators under these flavour symmetries, including symmetry breaking effects, and demonstrates their relevance for LHC phenomenology.

Findings

Operator classification under $U(3)^5$ and $U(2)^5$ symmetries

Counting of operators at different symmetry breaking orders

Application to high-$p_T$ analyses at the LHC

Abstract

We analyse how $U(3)^5$ and $U(2)^5$ flavour symmetries act on the Standard Model Effective Field Theory, providing an organising principle to classify the large number of dimension-six operators involving fermion fields. A detailed counting of such operators, at different order in the breaking terms of both these symmetries, is presented. A brief discussion about possible deviations from these two reference cases, and a simple example of the usefulness of this classification scheme for high-$p_T$ analyses at the LHC, are also presented.