2008/10/16 by M. Kachelriess, M. Kachelrieß, Kachelriess, M.
Physics and Astronomy · #Astrophysics (astro-ph) #Astrophysics and Cosmic Phenomena #Dark Matter and Cosmic Phenomena #FOS: Physical sciences #High Energy Physics - Phenomenology (hep-ph) #Particle physics theoretical and experimental studies #astro-ph #hep-ph
paper · pdf · doi:10.48550/arxiv.0810.3017
10 pages, 6 eps figures, invited talk at XXth Rencontres de Blois "Challenges in Particle Astrophysics"; v2: PAO photon limit corrected
openalex publication_date 2008/10/16 · arxiv created 2008/10/23 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The motivation and the current status of top-down models as sources of ultrahigh energy cosmic rays (UHECR) are reviewed. Stimulated by the AGASA excess, they were proposed as the main source of UHECRs beyond the GZK cutoff. Meanwhile searches for their signatures have limited their contribution to the UHECR flux to be subdominant, while the theoretical motivation for these searches remained strong: Topological defects are a generic consequence of Grand Unified Theories and superheavy particles are a creditable dark matter candidate. While Fermi/GLAST results should help to improve soon bounds on topological defects from the diffuse gamma-ray background, the most promising detection method are UHE neutrino searches. Superheavy dark matter can be restricted or detected by its characteristic galactic anisotropy combined with searches for UHE photons.