# Constraints on the relaxion mechanism with strongly interacting vector-fermions

## TL;DR

This paper examines experimental constraints on strongly interacting vector-fermions within the relaxion mechanism, highlighting how lower confinement scales lead to increased tuning and constraints from various experiments.

## Contribution

It provides a detailed analysis of experimental bounds on minimal models of the relaxion mechanism with low confinement scales, emphasizing the tuning issues involved.

## Key findings

- Constraints tighten as confinement scale decreases
- Tuning becomes significant at confinement scales of a few tens of MeVs
- Electroweak and collider bounds strongly restrict parameter space

## Abstract

We study the experimental constraints on strongly interacting vector-fermions compatible with the relaxion mechanism and investigate any possible tuning. The focus is on a minimal model and low confinement scale. More precisely, we study bounds from electroweak precision tests, Higgs decay, Big Bang nucleosynthesis and direct collider searches. The effect of these new fermions on vacuum stability is also investigated. Combining our bounds, we show that the relaxion mechanism becomes increasingly constrained and fine-tuned as the confinement scale decreases. For example, a confinement scale of a few tens of MeVs would require tuning at the percent level.