Constraints on exotic particle masses from flavor violating charged lepton decays and the role of interference

TL;DR

This paper investigates how experimental bounds on charged lepton flavor violating decays constrain the masses of exotic particles, including scalars and vector bileptons, highlighting the importance of interference effects in these constraints.

Contribution

It introduces the role of interference effects in constraining exotic particle masses from lepton flavor violating decays, especially for doubly charged vector bileptons, extending previous analyses.

Findings

Experimental bounds set strong exclusion limits on exotic particle masses.

Interference effects can significantly alter these exclusion regions.

Constraints are stronger than previous flavor conserving bounds.

Abstract

Together with any Beyond the Standard Model ultraviolet complete, renormalizable model, one or several exotic particles are usually hypothesized. $C\!P$-even neutral and doubly-charged scalars are common, well known examples which can contribute to the seven 3-body Charged Lepton Flavor Violating decays. The experimental bounds on each Branching Ratio within this set of processes provide a good test for new physics that can induce powerful constraints on relevant parameter spaces. This is specially true for a third species of particle which, unlike the previous two, is a rare feature of renormalizable models: a doubly charged vector bilepton. We show how these purely leptonic bounds can indeed induce relevant exclusion regions for the corresponding particles masses, stronger than what have been considered in the literature for the alternative flavor conserving case, and examine how interference effects can influence these regions in a non-trivial way.