Dipole portal to heavy neutral leptons

TL;DR

This paper explores how neutrino dipole portals to heavy neutral leptons (HNLs) change their phenomenology, deriving constraints from multiple experiments and proposing future sensitivities, especially in relation to LSND and MiniBooNE anomalies.

Contribution

It introduces a comprehensive analysis of the neutrino dipole portal to HNLs, including constraints and future experimental sensitivities, which is a novel approach in HNL phenomenology.

Findings

Dipole portals significantly alter HNL phenomenology.

Current data strongly constrain dipole-induced explanations of LSND and MiniBooNE anomalies.

Future experiments like SHiP and Fermilab can test the remaining parameter space.

Abstract

We consider generic neutrino dipole portals between left-handed neutrinos, photons, and right-handed heavy neutral leptons (HNL) with Dirac masses. The dominance of this portal significantly alters the conventional phenomenology of HNLs. We derive a comprehensive set of constraints on the dipole portal to HNLs by utilizing data from LEP, LHC, MiniBooNE, LSND as well as observations of Supernova 1987A and consistency of the standard Big Bang Nucleosynthesis. We calculate projected sensitivities from the proposed high-intensity SHiP beam dump experiment, and the ongoing experiments at the Short-Baseline Neutrino facility at Fermilab. Dipole mediated Primakoff neutrino upscattering and Dalitz-like meson decays are found to be the main production mechanisms in most of the parametric regime under consideration. Proposed explanations of LSND and MiniBooNE anomalies based on HNLs with dipole-induced decays are found to be severely constrained, or to be tested in the future experiments.