Ultra-High Energy Cosmic Rays  

In General > s.a. [cosmic rays]; matter phenomenology in quantum gravity; modified lorentz symmetry.
* Status: At E 1018 eV, some events show directionality; The rate falls almost to zero at 1020 eV, but there may be about 5 events/km2/sr/cy at higher energies; 2003, Auger being built [@ news pw(03)oct]; 2004, The total number of events is 6 (11 in AGASA?), so the evidence may be considered flimsy, and there are systematics that are not understood, and might be settled by Auger project; 2005, AGASA actually has 59 events at E > 4 × 1019 eV, roughly isotropic, and Auger has started seeing UHECR showers; 2007, Pierre Auger shows that the very
largest of cosmic ray showers, those with an energy higher than 57 EeV, correlated pretty well with known AGN's.
@ Intros: Cronin et al SA(97)jan; O'Halloran et al PT(98)jan; Musser SA(99)jan; De Marco ap/05-in.
@ General references: Stecker PRL(98) [origin and propagation]; Bhattacharjee & Sigl PRP(00)ap/98; Frampton ap/98-in; Yoshida & Dai JPG(98)ap; Biermann et al ap/00-in [M87?]; Anchordoqui et al PRD(01)hp/00 [monopoles?]; Nagano & Watson RMP(00); Bertou et al IJMPA(00)ap; Billoir & Letessier-Selvon ap/00; Sigl ap/00-ln, Sci(01)ap, AP(02), AP(03); Olinto PRP(00)ap; Watson ap/01-in, CP(02); Sarkar hp/02-in; Dick et al ap/02-in [and dark matter]; Starobinsky & Tkachev JETPL(02)ap [theory]; Olinto NPPS(02)ap; Blasi ap/03-in; Sigl APPB(04)ap-in; Olinto ap/04-in; Stenkin NPPS(06)ap/04; Gaisser & Stanev NPA(06)ap/05; issue NPPS(06)151#1; Medina-Tanco ap/06-in; Kampert a0801-in [rev]; Kachelriess a0801-ln.
@ Composition: Abbasi et HiRes ApJ(05)ap/04; Allard et al a0805.
@ Sources: Blandford ap/99-in [acceleration]; Farrar ap/05 [5-event cluster]; Pierpaoli & Farrar ap/05 [galaxy clusters]; Jain & Panda ap/05 [not primordial black holes]; Erlykin & Wolfendale JPG(05)ap; Blasi MPLA(05)ap; Inoue ap/07-in; Auger Collaboration Sci(07)-a0711 + pw(07)nov + PT(08)jan [nearby AGNs]; Gorbunov et al a0804 [AGNs]; Moskalenko et al a0805-ApJ, Stanev a0805 [AGNs, criticism]; Nagar & Matulich A&A-a0806 [Auger, nearby radio galaxies].
@ Propagation: Wibig CEJP(04)ap [extragalactic magnetic fields]; Candia ap/04-PhD; Meli & Biermann ap/06/A&A [acceleration and shocks]; Ostapchenko ap/06-in [interactions, rev]; Aloisio et al a0706-in [in expanding universe]; De Marco et al JCAP(07) [numerical].

Observation > s.a. cosmic rays [detectors]; neutrinos.
* Oh-My-God-Particle: A 3.2 1020 eV particle event observed on Oct 15, 1991.
@ First events: Hayashida et al PRL(94) [AGASA, 1 event], PRL(96) + pn(96)jul [AGASA, 36 events, directionality].
@ Pierre Auger: Mantsch ap/06-in; Zech ap/06-in; Kampert ap/06-in; Vorobiov ap/06-in; Matthiae a0807-in.
@ Other status: Anchordoqui et al IJMPA(03)hp/02; Stecker JPG(03)ap; Kachelrieß CRP(04)hp-in; Stanev ap/04-ln; Bergman & Belz a0704-JPG [composition].
@ Spectrum: Pierre Auger ap/05-in; Letessier-Selvon ap/05-in [and anisotropy]; De Marco & Stanev PRD(05); Yamamoto for PA ap/06-in, a0707-in; Connolly et al PRD(06)ap [comparison of experiments]; Roth et Auger a0706-in.
@ Anisotropy: Anchordoqui et al PRD(03) [search]; HiRes collaboration ApJL(04)ap, NPPS(04)ap-in, ap/05 [none found]; Mollerach & Roulet JCAP(05) [serach method]; De Marco et al JCAP(06)ap/05 [simulations]; Kachelrieß & Serpico PLB(06) [Compton-Getting effect]; Mikhailov a0705-in; Kalashev et al a0710 [and space-based detectors].
@ Related topics: Illana et al PRD(07)hp/06 [new physics]; Pierre Auger a0712 [photons above 1019 eV].

GZK Effect and Puzzle
* GZK effect: Cosmic rays of energies above E > 5 1019 eV interact with the cmb and produce pions, losing 20% of their energy with a mean free path of 30 Mpc; Led to the prediction of a sharp cutoff (knee) in the number of cosmic rays above that energy.
* GZK puzzle: Cosmic rays at energies above the Greisen-Zatsepin-Kuzmin cutoff are not expected, but observed; 2007, Cutoff seen by Pierre Auger and HiRes experiments.
* Possible explanations: (2005 assessment) Superheavy relic particle decay (speculative); Topological defects (speculative); "Z-burst", + → Z resonance → decay (would produce too many photons); Lorentz invariance violation (speculative); Neutron stars; Active galactic nuclei; In the latter two cases, need magnetic fields to bend the cosmic rays and make them isotropic.
@ Puzzle, evidence: Takeda et al PRL(98); Bahcall & Waxman PLB(03)hp/02; Anchordoqui & Goldberg PLB(04) [analysis]; Kopenkin & Fujimoto PRD(05) [1975 event above the knee]; Abbasi et HiRes PRL(08)ap/07 [cutoff seen where expected].
@ Puzzle, proposals: Berezinsky et al PRL(97) [massive particle decay]; Coleman & Glashow hp/98 [Lorentz violation]; Anchordoqui et al PLB(00), PLB(00); Bertolami GRG(02) [preferred frames]; Amelino-Camelia IJMPD(03)ap/02 [DSR]; Svetlichny FPL(04)ht/03 [non-linear quantum mechanics]; Gupta PLB(04)ap/03 [and Lorentz violation]; Zachos MPLA(04), reply Chen & Yang MPLA(04) [re non-commutative proposal]; Wibig & Wolfendale ap/04 [drop not sharp]; Parizot ap/04-in [effect of turbulent B]; Albuquerque & Smoot APP(06)ap/05 [smearing]; Kersting ap/06 [discrete space]; Berezinsky et al PRD(06); Hess & Greiner ht/07 [non-Lorentz-violating extension]; Gelmini et al a0706; de Unánue et al MPLA(07) [n's rather than p's]; > s.a. quantum gravity phenomenology [lqg], topological defects.
@ Related topics: Aloisio & Berezinsky ap/05-in [anti-GZK effect]; Erlykin & Wolfendale JPG(06)ap/05 [knee].

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