# Neutrino counting experiments and non-unitarity from LEP and future experiments

## TL;DR

This paper investigates how neutrino counting experiments can constrain non-unitarity in the neutrino mixing matrix, providing new bounds from gamma processes and exploring future collider sensitivities to invisible Z decays.

## Contribution

It introduces new constraints on neutrino non-unitarity from gamma process measurements and assesses future collider capabilities for improved bounds via Z boson decay observations.

## Key findings

- New bounds on non-unitarity from gamma process data
- Projected improvements from future collider experiments
- Enhanced sensitivity to neutrino mixing deviations

## Abstract

Non-unitarity of the neutrino mixing matrix is expected in many scenarios with physics beyond the Standard Model. Motivated by the search for deviations from unitary, we study two neutrino counting observables: the neutrino-antineutrino gamma process and the invisible $Z$ boson decay into neutrinos. We report on new constraints for non-unitarity coming from the first of this observables. We study the potential constraints that future collider experiments will give from the invisible decay of the Z boson, that will be measured with improved precision.