Superheavy Supersymmetric Dark Matter for the origin of KM3NeT Ultra-High Energy signal

TL;DR

The paper introduces superheavy supersymmetric dark matter (SSDM), a multicomponent DM framework with a nearly degenerate SUSY spectrum, to explain the KM3NeT ultra-high-energy neutrino observed without a clear astrophysical source. Heavier components decay to lighter ones, producing a boosted neutrino flux with energy $E_ν \sim \Delta M_χ$, distributed isotropically due to cosmological redshift and a long lifetime $\tau_χ \sim 1$ Gyr. Production is non-thermal, via gravitational particle production at the end of inflation or Hawking evaporation of light primordial black holes, naturally yielding comparable abundances among degenerate components. The paper analyzes two decay channels—direct three-body decays producing neutrinos and Higgs, and two-body decays to sterile neutrinos with oscillations—showing that the resulting extragalactic neutrino flux can fit the KM3NeT signal while respecting gamma-ray constraints, with observable implications for UHECRs and future detectors.

Abstract

We propose an explanation for the recently reported ultra-high-energy neutrino signal at KM3NeT, which shows no clear association with known astrophysical sources. While decaying dark matter in the Galactic Center is a natural candidate, the observed arrival direction strongly suggests an extragalactic origin. We introduce a multicomponent dark matter scenario in which the components are part of a supermultiplet, with supersymmetry ensuring a nearly degenerate mass spectrum among the fields with different spins. In this setup, a cosmologically long-lived fermionic state decays into a slightly lighter bosonic dark matter state, producing a boosted neutrino spectrum with energy $E_ν\sim 100$ PeV, determined by the mass difference. The heavy-to-light decay occurs at a cosmological redshift of $z \sim \text{a few}$ or higher, leading to an isotropic directional distribution of the signal.

Figures (3)

• Figure 1: The angular distribution of galactic component of neutrino flux from conventional decaying Dark Matter using NFW(1,3,1.5) profile (Top) and the neutrino flux spectrum (Bottom). In the top panel, we show the $\mathcal{D}$-factor $\mathcal{D}(\psi) = \int \rho(l,\psi) \ dl$ on the Galatic coordinate map. Cyan dashed lines correspond to $\mathcal{D}(\psi)/\mathcal{D}(\psi_0) = 0.2,0.1,0.05$ from inner to outer contours where $\psi$ is the angle between Galactic Center and the direction of line-of-sight. Here we consider the cutoff angle $\psi_0 = 1^\circ$ for the normalization. We overlap the direction of KM3-250213A neutrino origin as a red-star marker whose position is $(l,b)=(216.06^\circ,-11.13^\circ)$ in the Galactic coordinates. In the bottom panel, we show galactic (dashed red) and extragalactic (dashed blue) contribution to neutrino flux, and observational constraints on the diffuse flux from IceCube IceCube:2020wumAbbasi:2021qfzIceCube:2021rpzIceCube:2018fhm, Auger PierreAuger:2023pjg and ANTARES ANTARES:2024ihw (gray lines).
• Figure 2: Scheme of a model for superheavy supersymmetric dark matter. The dark matter supermultiplet possesses a large supersymmetric mass term, $M_\chi$, with a small mass splitting induced by SUSY-breaking effects. This small mass splitting remains radiatively stable compared to the dark matter mass. Each component field contributes equally to the dark matter density through their supersymmetric production mechanism. The long-lived heavier component of the supermultiplet decays into the lightest one, emitting a highly energetic neutrino (directly, secondarily, or via oscillation) with energy $E_\nu \sim \Delta M_\chi \ll M_\chi$ at production time. Consequently, any late-time decay of $\chi$ and $\tilde{\chi}_2$ remains consistent with cosmological constraints on dark matter density.
• Figure 3: The landscape of total neutrino and gamma-ray fluxes from Scenario I ($\chi \to \tilde{\chi}_- + \nu_\alpha + h$) and Scenario II ($\chi \to \tilde{\chi}_- + \nu_s$ and $\nu_s \to \nu_\mu$ via oscillation). We show the total flux of neutrinos and gamma-rays in Scenario I as thick blue and thick red lines respectively. The total flux of neutrinos in Scenario II is shown as thick green line. In order to provide demonstrative examples, we choose the parameters as $M_\chi = 10^{16}$ GeV, $\Delta M_\chi = 3 \times 10^9$ GeV, $f_\chi = 0.6$, $\text{Br}_\nu = 10^{-2.6}$ for Scenario I, and $M_\chi = 6 \times 10^{12}$ GeV, $\Delta M_\chi = 5 \times 10^8$ GeV, $f_\chi =0.6$, $\text{Br}_\nu =10^{-4}$ for Scenario II. The lifetime of heavier component $\chi$ is always assumed to be $\tau_\chi \equiv \Gamma_\chi^{-1} = 1$ Gyr. For the details, see the main text. The upper limits on isotropic diffuse fluxes of gamma-rays (from H.E.S.S HESS:2016pst and Femri-LAT Fermi-LAT:2014ryh) and neutrinos (from ANTARES ANTARES:2024ihw, IC-HESE IceCube:2020wum, IC-NST Abbasi:2021qfz, IC-Glashow IceCube:2021rpz, IC-EHE IceCube:2018fhm and Auger PierreAuger:2023pjg) are shown as faint red and blue lines, respectively. The desired neutrino flux based on KM3NeT effective area is indicated by black and gray lines KM3NeT:2025npi. In Scenario I, gamma-ray flux without attenuation and electromagnetic cascade is shown as a dot-dashed red line for comparison. In Scenario II, we also show the case with $\text{Br}_\nu = 10^{-3}$ as upper thin green line.