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Neutrino Dipole Portal

Sin Kyu Kang, C. J. Ouseph

TL;DR

The Neutrino Dipole Portal proposes a minimal, predictive EFT in which a dimension-five transition dipole μ_{νN} couples active neutrinos to a heavy neutral lepton via the electromagnetic field, generating distinctive production and decay channels such as up-scattering, radiative decays, and Dalitz-like meson processes. The framework is embedded in SMEFT and compatible with UV completions, while its phenomenology spans laboratory experiments, astrophysical environments, and cosmology, with cross-cutting signatures in recoil spectra and displaced photons. A broad experimental program — from fixed-target and collider searches to CEνNS/NEES measurements and cosmological/astrophysical bounds — already constrains μ_{νN} down to ~10^{-11} μ_B for light N, with future facilities (SHiP, DUNE near detectors, XENONnT/LZ, Dresden-II/CONUS+, IceCube, LEP-like and LHC probes) poised to close remaining windows. The NDP thus offers a simple, testable portal at the intersection of particle physics, astrophysics, and cosmology, where complementary probes will either exclude large swaths of parameter space or provide a first window into beyond-Standard-Model dynamics involving neutrino electromagnetic interactions.

Abstract

The neutrino dipole portal (NDP) is a minimal and predictive extension of the Standard Model, in which a transition magnetic moment operator couples an active neutrino to a heavy neutral lepton via the electromagnetic field. This higher-dimensional interaction gives rise to distinctive processes such as neutrino up-scattering, radiative decays, meson transitions, and modifications of recoil spectra, offering multiple avenues for discovery. In this review, we discuss the theoretical foundations of the NDP, its ultraviolet completions, and the associated production and decay mechanisms across laboratory, astrophysical, and cosmological settings. Current constraints arise from accelerator searches, recoil-based detectors, collider studies, and high energy neutrino observatories, complemented by robust bounds from Big Bang Nucleosynthesis, the Cosmic Microwave Background, and supernova cooling. Future experimental and observational efforts, including next-generation neutrino experiments, multi-ton dark matter detectors, and improved cosmological and astrophysical probes, are anticipated to test the remaining allowed regions. The NDP thus provides a simple, well-motivated, and broadly testable framework at the intersection of particle physics, astrophysics, and cosmology.

Neutrino Dipole Portal

TL;DR

The Neutrino Dipole Portal proposes a minimal, predictive EFT in which a dimension-five transition dipole μ_{νN} couples active neutrinos to a heavy neutral lepton via the electromagnetic field, generating distinctive production and decay channels such as up-scattering, radiative decays, and Dalitz-like meson processes. The framework is embedded in SMEFT and compatible with UV completions, while its phenomenology spans laboratory experiments, astrophysical environments, and cosmology, with cross-cutting signatures in recoil spectra and displaced photons. A broad experimental program — from fixed-target and collider searches to CEνNS/NEES measurements and cosmological/astrophysical bounds — already constrains μ_{νN} down to ~10^{-11} μ_B for light N, with future facilities (SHiP, DUNE near detectors, XENONnT/LZ, Dresden-II/CONUS+, IceCube, LEP-like and LHC probes) poised to close remaining windows. The NDP thus offers a simple, testable portal at the intersection of particle physics, astrophysics, and cosmology, where complementary probes will either exclude large swaths of parameter space or provide a first window into beyond-Standard-Model dynamics involving neutrino electromagnetic interactions.

Abstract

The neutrino dipole portal (NDP) is a minimal and predictive extension of the Standard Model, in which a transition magnetic moment operator couples an active neutrino to a heavy neutral lepton via the electromagnetic field. This higher-dimensional interaction gives rise to distinctive processes such as neutrino up-scattering, radiative decays, meson transitions, and modifications of recoil spectra, offering multiple avenues for discovery. In this review, we discuss the theoretical foundations of the NDP, its ultraviolet completions, and the associated production and decay mechanisms across laboratory, astrophysical, and cosmological settings. Current constraints arise from accelerator searches, recoil-based detectors, collider studies, and high energy neutrino observatories, complemented by robust bounds from Big Bang Nucleosynthesis, the Cosmic Microwave Background, and supernova cooling. Future experimental and observational efforts, including next-generation neutrino experiments, multi-ton dark matter detectors, and improved cosmological and astrophysical probes, are anticipated to test the remaining allowed regions. The NDP thus provides a simple, well-motivated, and broadly testable framework at the intersection of particle physics, astrophysics, and cosmology.
Paper Structure (30 sections, 71 equations, 7 figures)

This paper contains 30 sections, 71 equations, 7 figures.

Table of Contents

  1. Introduction
  2. Theoretical Framework
  3. Production Mechanisms
  4. Neutrino Up-scattering via the Dipole Portal
  5. Meson-Induced Production
  6. Two-Body Decay of Vector Mesons
  7. Radiative Dalitz-like Decays of Neutral Mesons
  8. Weak Three-Body Decays via Off-Shell Neutrino
  9. Production at Colliders
  10. Experimental Signatures
  11. Radiative Deacy Signatures
  12. Recoil Spectrum Distortions
  13. NEES
  14. CE$\nu$NS
  15. Experimental Searches and Constraints
  16. ...and 15 more sections

Figures (7)

  • Figure 1: Tree level neutrino scattering process with a final state photon, arising from dipole portal to HNL Magill:2018jla.
  • Figure 2: Representative meson decay topologies induced by the NDP, taken from Ref. Barducci:2023hzo : (a) Two-body vector meson decay, (b) Radiative Dalitz-like neutral meson decay, and (c) Weak three-body charged meson decay.
  • Figure 3: Constraints on the $(M_N,\,\mu_{\nu_e N})$ parameter space for $\nu_e$. Left: Current $90$–$95\%$ C.L. exclusions from reactor NEES (CONUS CONUS:2020skt, Dresden-II AristizabalSierra:2022axl, GEMMA Beda:2012zzBeda:2013mta, TEXONO Deniz:2009mu), solar NEES searches (Borexino Agostini:2017ixy, SK Super-Kamiokande:2016yck), LSND LSND:2001akn, and dark matter detectors (XENONnT XENON:2024ijk, PandaX–4T PandaX:2024muv, LZ LZ:2022lsv). Right: Same as left panel, with the addition of the new CONUS+ bound (including CE$\nu$NS and NEES) CONUS:2024lnuDeRomeri:2025csu, and projected sensitivities from DUNE–ND DUNE:2015lol, SHiP SHiP:2015vad, FASER$\nu$2 FASER:2022hcn, and FLArE–10/100 Cerci:2021nlb.
  • Figure 4: Constraints on the $(M_N,\,\mu_{\nu_\mu N})$ parameter space for $\nu_\mu$. Left: Current $90$–$95\%$ C.L. exclusions from CHARM–II CHARM-II:1989srx, NOMAD NOMAD:1997pcg, MINER$\nu$A MINERvA:2022vmb, Borexino, and MiniBooNE/LSND, along with CE$\nu$NS and NEES limits from Fig. \ref{['fig:res_sterile_dipole_e']}. Right: Same as the left panel, with the addition of projected sensitivities from T2K+T2K–II T2K:2019jwa, DUNE–ND DUNE:2015lol, SHiP SHiP:2018xqw, FASER$\nu$2 FASER:2022hcn, FLArE–10/100 Cerci:2021nlb, and IceCube IceCube:2016umi. ROIs motivated by the MiniBooNE anomaly MiniBooNE:2018esg are also shown.
  • Figure 5: Constraints on the $(M_N,\,\mu_{\nu_\tau N})$ parameter space for $\nu_\tau$. Left: Existing $90$–$95\%$ C.L. exclusions from DONUT DONUT:2001zvi, solar NEES searches, reactor and CE$\nu$NS searches with xenon detectors, and radiative decay bounds from solar/atmospheric neutrinos. Right: Same as the left panel, with the addition of the projected reach of DUNE–FD Schwetz:2020xra, SHiP SHiP:2018xqw, FASER$\nu$2 FASER:2022hcn, FLArE–10/100 Cerci:2021nlb, and IceCube IceCube:2016umi, which provide sensitivity to long-lived radiative decays in the $\nu_\tau$ sector.
  • ...and 2 more figures