Searching for Lepton Flavor Violation at a Future High Energy Electron-Positron Collider

TL;DR

This paper explores the potential of future high-energy electron-positron colliders to detect lepton flavor violation, focusing on the process e+e- -> e tau, and shows they can significantly improve existing bounds on new physics scales.

Contribution

It demonstrates that future colliders can surpass current tau decay constraints in probing lepton flavor violation via contact interactions.

Findings

Collider searches can improve bounds to over 11 TeV at 500 GeV.

At 3 TeV, bounds can reach beyond 35 TeV.

e-e- colliders can provide even stronger constraints.

Abstract

We consider theories where lepton flavor is violated, in particular concentrating on the four fermion operator consisting of three electrons and a tau. Strong constraints are available from existing searches for tau -> eee, requiring the scale of the contact interaction to be less than ~(9 TeV)^-2. We reexamine this type of physics, assuming that the particles responsible are heavy (with masses greater than ~TeV) such that a contact interaction description continues to be applicable at the energies for a future e+e- collider. We find that the process e+e- -> e tau can be a very sensitive probe of this kind of physics (even for very conservative assumptions about the detector performance), already improving upon the tau decay bounds to less than ~(11 TeV)^-2 at collider energy sqrt(s) 500 GeV, or reaching beyond ~(35 TeV)^-2 for sqrt(s) = 3 TeV. Even stronger bounds are possible at e-e- colliders in the same energy range.