Are small neutrino masses unveiling the missing mass problem of the Universe?

TL;DR

The paper tackles the coincidence between the origin of neutrino masses and the nature of dark matter by proposing a minimal low-energy framework with a single interaction term $L_I$ that links the two sectors. Neutrino masses are generated at one loop and are Majorana, while the scalar DM candidate $φ$ (the SLIM) annihilates predominantly into neutrino pairs, fixing the relic abundance via $⟨σ v_r⟩$. A compact relation $m_{ν_L} \simeq \sqrt{⟨σ v_r⟩/(128 π^3)} \, m_N^2 (1 + m_φ^2/m_N^2) \ln(Λ^2/m_N^2)$ arises, tying the DM cross section to the neutrino mass scale and predicting $m_N$ in the MeV range with $m_φ$ below ~10 MeV. This MeV-scale DM can also account for the 511 keV emission in the Galactic center and potentially relate to LSND, suggesting a fundamental role for dark matter beyond a relic. The model remains compatible with cosmology and current constraints and points to low-energy experiments and precise neutrino mass measurements as potential tests.

Abstract

We present a scenario in which a remarkably simple relation linking dark matter properties and neutrino masses naturally emerges. This framework points towards a low energy theory where the neutrino mass originates from the existence of a light scalar dark matter particle in the MeV mass range. A very surprising aspect of this scenario is that the required MeV dark matter is one of the favoured candidates to explain the mysterious emission of 511 keV photons in the centre of our galaxy. A possible interpretation of these findings is that dark matter is the stepping stone of a theory beyond the standard model instead of being an embarrassing relic whose energy density must be accounted for in any successful model building.

Figures (2)

• Figure 1: In the scenario discussed here, left-handed neutrinos acquire a very small mass term due to their interactions with a SLIM and a $N$ particle. This mass term is of Majorana type owing to the Majorana nature of $N$.
• Figure 2: Here are the three diagrams corresponding to the main SLIM annihilation channels. These three diagrams are very similar to Fig. \ref{['neutrino1']}. They involve the same couplings $g$ and rely on the exchange of the particle $N$. The important point is that the first diagram exactly corresponds to Fig. \ref{['neutrino1']} if one joins the legs of the two SLIM particles in the initial state and rotates the diagram.