Constraining lepton flavor violating SMEFT $2q2\ell$ operators from low-energy cLFV processes

TL;DR

This paper uses low-energy charged lepton flavor-violating processes to constrain lepton flavor violating operators in the Standard Model Effective Field Theory, providing bounds on new physics effects involving quarks and leptons.

Contribution

It systematically analyzes low-energy cLFV processes within SMEFT to derive the strongest constraints on $2q2\,\ell$ operators, considering operator correlations.

Findings

Established bounds on $2q2\ell$ operators from low-energy cLFV data.

Identified key operators contributing to cLFV processes.

Provided a framework for future constraints on SMEFT operators.

Abstract

Charged lepton flavour-violating (cLFV) processes, which are definite proof of new physics beyond the Standard Model, have remained elusive experimentally till now. Effective Field Theory (EFT) has been very useful in providing information about such new physics through the higher-dimensional operators. These operators respect SM gauge invariance, and they are suppressed by appropriate powers of the energy scale $\Lambda$. In regard to lepton flavour violating (LFV) processes, the Standard Model Effective Field Theory (SMEFT) is shown to be a useful tool for estimating any new physics effect at the scale $\Lambda$. It is worth noticing that a large class of cLFV processes involve both quarks and leptons and thus low-energy observables play a significant role in providing bounds on lepton-flavour-violating 2-quark-2-lepton ($2q2\ell$) operators. Therefore, in this work, we have collected several low-energy cLFV processes that can be addressed within the SMEFT framework and also collected the set of operators responsible for such processes. Keeping in mind the correlation that exists among the SMEFT operators, we want to extract the strongest constraints on these $2q2\ell$ operators.