Improved Bounds and Global Fit of Flavor-Violating Charged Lepton Yukawa Couplings post LHC

TL;DR

This paper updates and refines the bounds on flavor-violating charged lepton Yukawa couplings using LHC data, linking these bounds to new physics scales and providing future experimental projections.

Contribution

It provides the most recent bounds on flavor-violating Higgs couplings, compares direct and indirect constraints, and translates these bounds into limits on new physics scales within SMEFT.

Findings

LHC bounds on FV couplings are stronger than indirect constraints.

Bounds on couplings range from 10^{-3} to 10^{-6}.

New physics scale is constrained between 10 and 100 TeV.

Abstract

Higgs couplings to charged leptons form an important measurement to understand not only the Standard Model (SM), but also physics Beyond Standard Models (BSM). In this work, we update the bounds on the Flavor-Violating (FV) Higgs couplings to charged leptons. We find that the bounds on the size of the couplings could range between $\sim \mathcal{O}(10^{-3}) - \mathcal{O}(10^{-6})$. In fact, the direct constraints from LHC are much stronger than those inferred indirectly from rare decays in the $\tau$-$\mu$ and $\tau$-$e$ sector. We also match these bounds to the SM Effective Field Theory (SMEFT) and find lower limits on the scale of New Physics (NP). We find that the scale of NP ranges between $\sim \mathcal{O}(10) - \mathcal{O}(100)$ TeV. We also present future projections for some upcoming experiments. We find that the current bounds on the couplings to $\mu$-$e$ are stronger than all future projections.