1999/10/13 by Thomas J. Weiler, Weiler, Thomas J.
Physics and Astronomy · #Astrophysics (astro-ph) #FOS: Physical sciences #High Energy Physics - Phenomenology (hep-ph) #astro-ph #hep-ph
paper · pdf · doi:10.48550/arxiv.hep-ph/9910316
22 pages, 1 figure, Invited talk at "Beyond the Desert 99", Ringberg Castle, Tegernsee, Germany, June 6-12, 1999
arxiv created 1999/10/13 · arxiv updated 2009/11/30
The observation of cosmic--ray events above the Greisen-Kuzmin-Zatsepin (GZK) cutoff of ∼ 5× 1019 eV challenges orthodox modeling. We discuss a possible solution which uses standard hot Big Bang cosmology and Standard Model (SM) particle physics augmented only by \lsim eV neutrino masses as suggested by solar, atmospheric, and terrestrial neutrino detection. In this scheme, cosmic ray neutrinos from distant, highest-energy sources annihilate resonantly on the relic-neutrino background to produce Z-bosons. The highly-boosted (γZ∼ 1011) Z's instantly decay, producing "Z-bursts" of highly-collimated jets of hadrons and photons. The burst content includes, on average, twenty photons and two nucleons with super-GZK energies. We show that the probability for each neutrino with energy within a fraction ΓZ/MZ of the resonant value ER=4(eV/mν)× 1021 eV to annihilate within the halo of our galactic supercluster is likely within an order of magnitude of 1%. Depending on the magnitude of the cosmic neutrino flux above 1020 eV, this "local" rate for primary production may be high enough to produce the cosmic ray events observed above the GZK cutoff. Several tests of this Z-burst hypothesis for generating super-GZK events are presented, including (i) a new cutoff energy at ER; (ii) a large γ/p ratio for primaries near the upper end of the spectrum; (iii) directional pairing of events, and pointing to their cosmic sources; and (iv) a neutrino flux above the GZK cutoff energy which is possibly measurable directly in proposed \gsim 1011 ton cosmic-ray detectors.