Long-Lived-Particle Signals of a Composite Hidden Sector through the Neutrino Portal

TL;DR

This paper investigates long-lived particles arising from a composite hidden sector coupled via the neutrino portal, analyzing their signals and potential detection at future colliders and beam dump experiments.

Contribution

It introduces a model where a conformal hidden sector with a low compositeness scale produces long-lived scalar states detectable through neutrino portal interactions.

Findings

FASER, SHiP, and Belle II can probe significant unexplored parameter space.

Long-lived scalar states are naturally suppressed in decay rates due to angular momentum.

Current constraints on the model are established.

Abstract

We explore the signals of a scenario in which the composite states of a strongly coupled hidden sector couple to the Standard Model through the neutrino portal, giving rise to the neutrino masses. We consider a framework in which the hidden sector is conformal in the ultraviolet and the compositeness scale lies below the weak scale. If the lightest composite state in the hidden sector is a scalar, its decay rate back to the Standard Model is suppressed by angular momentum considerations and can naturally be small, giving rise to long-lived particle signals. We determine the current constraints on this class of models and explore the reach of future collider and beam dump searches. We find that FASER, SHiP, and Belle II can potentially probe a significant part of the unexplored parameter space.