Searches for dark matter decay with ultrahigh-energy neutrinos endure backgrounds

Abstract

Next-generation ultra-high-energy (UHE) neutrino telescopes, presently under planning, will have the potential to probe the decay of heavy dark matter (DM) into UHE neutrinos, with energies in excess of 10 7 GeV. Yet, this potential may be deteriorated by the presence of an unknown background of UHE neutrinos, cosmogenic or from astrophysical sources, not of DM origin and seemingly large enough to obscure the DM signature. We show that leveraging the angular and energy distributions of detected events safeguards future searches for DM decay against such backgrounds. We focus on the radio-detection of UHE neutrinos in the planned IceCube-Gen2 neutrino telescope, which we model in state-of-the-art detail. We report promising prospects for the discovery potential of DM decay into UHE neutrinos, the measurement of DM mass and lifetime, and limits on the DM lifetime, despite the presence of a large background, without prior knowledge of its size and shape.searches widened after the discovery by the IceCube neutrino telescope of high-energy neutrinos of cosmic origin, with energies between 10 TeV and 10 PeV [30][31][32][33][34][35][36]. In fact, initially the discovery led to speculation that heavy DM decaying to neutrinos could explain their flux in the 10-100 TeV range [37-47]. Nowadays, more conventional astrophysical explanations are favored [48-50], but Ice-Cube observations still set competitive bounds on the DM lifetime and self-annihilation cross section for DM masses below 10 PeV [17, 51, 52]. These bounds are complementary to the ones obtained from gamma-ray observations in a similar mass range; see, e.g., Refs. [17, 53] In the next decade, a host of new neutrino telescopes, presently in different stages of planning, design, and prototyping, will target the long-sought discovery of UHE neutrinos, between 100 PeV and 10 EeV, that were first predicted in 1969 [54]. They include Auger-Prime [55], BEACON [56], EUSO-SPB2 [57], GCOS [58], GRAND [59], POEMMA [60], PUEO [61], RNO-G [62], TAROGE [63], and the radio array of IceCube-Gen2, the envisioned upgrade of IceCube [64]. Ultra-high neutrinos will bring new insight into astrophysics [65-67] and fundamental physics [66-71]. In particular, they will allow us to test the decay of heavier DM particles, with masses from 10 PeV to 100 EeV; see, e.g., Refs. [17, 29, 72]. However, the capacity of UHE neutrino telescopes to probe DM decay critically depends on an unknown quantity: the diffuse flux of UHE neutrinos that do not originate from DM decay, and that acts as a background to DM searches. If this background is large, it could obscure more subtle signatures of neutrinos from DM decay. These background neutrinos-hereafter dubbed "non-DM neutrinos"-are expected from the interaction of ultra-high-energy cosmic-ray (UHECRs) with ambient matter or radiation inside the extragalactic astrophysical sources where they are accelerated-i.e., astrophysical neutrinos-or with cosmic photon backgrounds during their propagation to Earth-i.e., cosmogenic neutrinos [54, 73, 74]. We e...

Constraining decaying very heavy dark matter from galaxy clusters with 14 year Fermi-LAT data

“…Dedicated analyses of multi-messenger astrophysical data have set strongest constraints on the lifetime of very heavy dark matter (VHDM) with masses up to EeV or even the GUT (Grand Unified Theory) scale (∼10 16 GeV) [43,[56][57][58][59][60]. The IceCube Neutrino Observatory [61][62][63] and the large high altitude air shower observatory (LHAASO) [64] also searched for decaying dark matter with masses above PeV and set competitive limits.…”

High-Energy and Ultra-High-Energy Neutrino Astrophysics

“…[309][310][311][312]), especially in the case of primary decay to neutrinos. Furthermore, the sensitivity of the future radio telescopes to the diffuse flux of UHE neutrinos will allow them to extend these bounds into the region of heavier masses, above tens of PeV [309,[313][314][315].…”