Lepton-flavour-violating gluonic operators: constraints from the LHC and low energy experiments

TL;DR

This paper recasts LHC data to set new limits on lepton-flavour-violating gluonic operators, providing the most stringent constraints for most cases and comparing them with low-energy experiment results.

Contribution

It offers the first comprehensive recasting of LHC analyses to constrain dimension-8 lepton-flavour-violating gluonic operators, improving existing bounds.

Findings

LHC data constrains operator scale to >0.5-1.6 TeV.

Most stringent limits for non-parity-conserving operators.

Low-energy experiments still provide the strongest bounds for certain operators.

Abstract

Effective operators provide a model-independent description of physics beyond the stan- dard model that is particularly useful given the absence of any signs of new physics at the Large Hadron Collider (LHC). We recast previous LHC analyses to set limits on lepton-flavour-violating gluonic effective operators of dimension 8 and compare our results to existing limits from low-energy precision experiments. Current LHC data constrains the scale $\Lambda$ of the effective operators to be larger than $\Lambda\gtrsim 0.5 - 1.6$ TeV depending on the flavour and thus provides the most stringent limit for all operators apart from parity-conserving operators of the form $GG\bar\mu P_{L,R} e$, where $\mu - e$ conversion in nuclei poses the most stringent constraint.