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.
Highlights
The standard model of particles and fields (SM) shows remarkable resilience under the scrutiny of numerous particle physics experiments
In this paper we have considered a variety of phenomenological consequences of a massive Dirac particle, that has a dipole portal d to the SM neutrinos and the photon, as a main source of production and decay of heavy neutral leptons (HNL)
The Dirac nature of the mass of N is dictated by the arguments of the neutrino mass generation. Different variants of such models have been proposed in the past, as a way of mimicking the excess of neutrino signals observed at LSND and MiniBooNE
Summary
The standard model of particles and fields (SM) shows remarkable resilience under the scrutiny of numerous particle physics experiments. The necessary ingredient of this proposal is a new fermionic state N in the 10-to-few100 MeV mass range and the dipole coupling in Eq (1) This coupling mediates a relatively prompt decay of N to a normal neutrino and a photon, a signature that can be confused with the “normal” electron or positron final state in charged current events [4,5]. Whether this model can simultaneously account for both anomalies without running into problems with other constraints remain an open issue
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