Superheavy supersymmetric dark matter as the origin of the KM3NeT ultrahigh energy signal

We propose an explanation for the recently reported ultrahigh-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 <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:msub> <a:mi>E</a:mi> <a:mi>ν</a:mi> </a:msub> <a:mo>∼</a:mo> <a:mn>100</a:mn> <a:mtext> </a:mtext> <a:mtext> </a:mtext> <a:mi>PeV</a:mi> </a:math> , determined by the mass difference. The heavy-to-light decay occurs at a cosmological redshift of <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:mi>z</c:mi> <c:mo>∼</c:mo> <c:mrow> <c:mi mathvariant="normal">a</c:mi> <c:mtext> </c:mtext> <c:mi>few</c:mi> </c:mrow> </c:math> or higher, leading to an isotropic directional distribution of the signal.