Non-Standard Neutrino Interactions at Neutrino Experiments and Colliders

TL;DR

The paper systematically compares neutrino NSI constraints with collider bounds for minimal, explicit mediator models—spin-0 leptoquarks, spin-1 gauge bosons, and spin-1/2 heavy neutral leptons—highlighting where neutrino experiments provide unique sensitivity versus where high-energy colliders dominate. By mapping low-energy NSIs to SMEFT operators and then to explicit mediators, the authors show that for most models at TeV scales, LHC (and HL-LHC) constraints surpass NSI bounds, while muon-philic leptoquarks and certain HNL scenarios with e/μ mixing can yield competitive or stronger neutrino-based limits, albeit with ND systematics playing a crucial role. They also explore dimension-8 operator scenarios and illustrate that cancellations required to evade dimension-6 constraints tend to be ineffective at collider energies, keeping collider data as a robust probe. Overall, the work underscores the complementarity between neutrino experiments and collider searches for NSIs and outlines how future facilities (HL-LHC, FCC/e+, muon colliders) will further tighten the available parameter space.

Abstract

The impact of new physics on the interactions of neutrinos with other particles can be parametrized by a set of effective four-fermion operators called non-standard neutrino interactions (NSIs). This NSI framework is useful for studying the complementarity between different types of neutrino experiments. In this work, we further compare the reach of neutrino experiments with high-energy collider experiments. Since high-energy colliders often probe the mass scale associated with the four-fermion operators, the effective field theory approach becomes invalid and explicit models must be utilized. We study a variety of representative simplified models including new U(1) gauge bosons, scalar leptoquarks, and heavy neutral leptons. For each of these, we examine the model parameter space constrained by NSI bounds from current and future neutrino experiments, and by data from the Large Hadron Collider and planned electron-positron and muon colliders. We find that in the models we study, with the possible exceptions of muon-philic leptoquarks and heavy neutral leptons mixing with electron or muon neutrinos, collider searches are more constraining than neutrino measurements. Additionally, we briefly comment on other model building possibilities for obtaining models where neutrino experiments are most constraining.

Figures (8)

• Figure 1: Comparison of current and future bounds (95% C.L.) from neutrino experiments and colliders on $g_{Z'}/m_{Z'}$ for the $Z'_{B-L}$ model. See text for more details. The shaded region displays the perturbativity bound.
• Figure 2: Comparison of current and future bounds (95% C.L.) from neutrino experiments and colliders on $g_{Z'}/m_{Z'}$ for the $Z'$ model with axial charges.
• Figure 3: Bounds on $|\lambda_{\mu d}|/m_\omega$ for the scalar leptoquark $\Omega$ with $\lambda_{\mu d} \neq 0$, $\lambda_{ed} = \lambda_{\tau d}=0$ from current and future neutrino and collider experiments (95% C.L.). The shaded region displays the perturbativity bound.
• Figure 4: Bounds on $|\lambda_{\tau d}|/m_\omega$ for the scalar leptoquark $\Omega$ with $\lambda_{\tau d} \neq 0$, $\lambda_{ed} = \lambda_{\mu d}=0$ from current and future neutrino and collider experiments (95% C.L.). The shaded region displays the perturbativity bound.
• Figure 5: Bounds on the mixing angle between active neutrinos and a HNL $N$ from current and future neutrino and collider experiments (95% C.L.) for different flavor patterns: $N$ mixing only with $\nu_e$ (a), only with $\nu_\mu$ (b), and only with $\nu_\tau$ (c). The shaded regions show the perturbativity bounds.