High-energy cLFV at $\mu$TRISTAN: HNL extensions of the Standard Model

TL;DR

This paper evaluates the potential of the future $mbda$TRISTAN collider to detect heavy neutral lepton-induced charged lepton flavor violation, showing it could surpass low-energy experiments for certain flavor violations.

Contribution

It provides the first detailed analysis of $mbda$TRISTAN's sensitivity to HNL-induced charged lepton flavor violation and compares it with existing low-energy constraints.

Findings

$mbda$TRISTAN can significantly improve detection prospects for $embda$ and $mbdambda$ flavor violations.

The collider's sensitivity to $mbdambda$ processes exceeds low-energy probes by several orders of magnitude.

Results highlight the importance of collider searches in exploring HNL models.

Abstract

Within the context of heavy neutral lepton (HNL) extensions of the Standard Model, we compute the cross-sections for $\mu^+ e^-\to \ell_\alpha^+\ell_\beta^-$ scattering, as well as several angular observables. In particular, we investigate the future sensitivity of a $\mu$TRISTAN collider in discovering such charged lepton flavour violating processes and the potential constraining power of these searches on the parameter space of HNL models. Our results show that while low-energy probes of $\mu-e$ flavour violation do offer the most promising potential, the prospects for $e\tau$ and $\mu\tau$ flavour violation searches at $\mu$TRISTAN can exceed those of related low-energy probes (as well as flavour violating $Z$-pole processes at FCC-ee) by several orders of magnitude.