Probing Neutrino Compositeness with Invisible and Displaced Signals

TL;DR

This paper investigates how neutrinos interacting with a sterile sector could produce unique signals like dark jets and displaced vertices in high-energy experiments, offering new ways to test neutrino compositeness beyond current constraints.

Contribution

It introduces a novel portal involving a sterile sector leading to distinctive collider signatures, expanding the experimental search strategies for neutrino compositeness.

Findings

Dark resonances can increase neutral-current to charged-current ratios.

Dark states can produce displaced vertices and emerging jets.

High-energy neutrino beams can probe parameter space beyond existing constraints.

Abstract

We explore the possibility that neutrinos couple to an interacting sterile sector, providing a novel portal that generalizes the heavy neutral lepton portal to a composite setting. For a low confinement scale, high-energy neutrino beams can disintegrate into collimated sprays of hidden states, referred to as dark jets. This dynamics gives rise to two characteristic signatures in high energy neutrino beams. First, long-lived dark resonances can enhance the neutral-current to charged-current ratio. Second, shorter-lived dark states produced in neutrino neutral currents can produce single or multiple displaced vertices and even emerging jets, depending on the kinematics. These signals probe regions of parameter space beyond existing constraints from meson, electroweak, and Higgs decays, as well as from searches for displaced decays at beam dump experiments. We study these phenomena within broad classes of ultraviolet completions and identify scenarios in which high-energy neutrino beams provide leading sensitivity to neutrino compositeness. Such scenarios generically induce higher-dimensional contact interactions, which we classify and study alongside their complementary experimental signatures. Finally, we outline an experimental program spanning both the intensity and energy frontiers. Near-term neutrino facilities (DUNE, FPF) and running flavor experiments (LHCb, Belle II) can probe neutrino compositeness through neutrino disintegration into dark jets and displaced B-meson decays. Future colliders, particularly the Future Circular Collider (FCC-ee), will ultimately provide the strongest sensitivity to the compositeness scale via displaced Z decays.