ultra high energy cosmic rays: theoretical aspects Daniel De Marco Bartol Research Institute University of Delaware

plan observations & open issues origin of UHECRs propagation: the GZK feature small scale anisotropies UHECRs, -rays and s

indirect observation (EAS) direct observation (1 particle per km2--century)

many joules in one particle indirect observation (EAS) direct observation (1 particle per km2--century) UHECR many joules in one particle

UHECRs: observations spectrum composition AGASA HiRes Auger arrival directions high energy AGASA composition Ostapchenko, Heck 2005 arrival dirs. low energy AGASA

UHECRs: observations two (separate) issues production propagation AGASA HiRes Auger spectrum arrival directions high energy AGASA two (separate) issues production for astrophysical accelerators it is challenging to accelerate particles to such high energies. propagation GZK feature in the energy spectrum due to the interactions with the photons of the CMB composition Ostapchenko, Heck 2005 arrival dirs. low energy end of the CR spectrum at some high energy strong flux suppression around 5 x 1019eV AGASA

origin of UHECRs bottom-up top-down the energy flux embedded in a macroscopic motion or in magnetic fields is partly converted into energy of a few very high energy particles. Shock acceleration at either Newtonian or Relativistic shocks. Composition: nucleons (nuclei) autolimiting: Emax ≤ Ze B L

hillas plot Emax ≤ Ze B L Hillas 1984 accounting for energy losses the situation is even more difficult lines: 1020 eV Olinto 2000

origin of UHECRs bottom-up top-down the energy flux embedded in a macroscopic motion or in magnetic fields is partly converted into energy of a few very high energy particles. Shock acceleration at either Newtonian or Relativistic shocks. Composition: nucleons (nuclei) autolimiting: Emax ≤ Ze B L particle physics inspired models UHECRs are generated by the decay of very massive particles mX » 1020 eV originating from high-energy processes in the early universe. Topological Defects or SMRP flatter spectra Composition: dominated by photons Constraints from the diffuse gamma rays flux measured by EGRET around 100 GeV

propagation of UHECRs: protons redshift losses pair production (Eth ~ 5x1017 eV) pUHE +CMB  N + e+ + e- pion production (Eth ~ 7x1019 eV) pUHE +CMB  N +  high inelasicity (20 – 50%) loss lengths GZK suppression: loss length @ 5x1019 eV = 1 Gpc loss length @ 1020 eV = 100 Mpc

GZK feature: single source modification factor: observed spectrum / injection spectrum bump suppression

similar conclusions for nuclei and gamma rays: CRs can not reach us at UHE if they are generated at distances larger than about 100 Mpc (except neutrinos, violations of LI and so on) if the sources are uniformly distributed in the universe we should expect a suppression in the flux of UHECRs around 1020 eV

actual discrepancies more like ~3 and ~2 AGASA & HiRes AGASA claims noGZK at 4 HiRes claims GZK at 4 a factor 2 in the flux HiRes: GZK AGASA: no GZK actual discrepancies more like ~3 and ~2 DDM, Blasi, Olinto 2003, 2005

systematic errors (?) AGASA -15% HiRes +15% agreement at low energy less disagreement at high energy how much?? ~2 DDM, Blasi, Olinto 2003, 2005 DDM, Stanev 2005

some AGASA spectra DDM, Blasi, Olinto 2005

both AGASA and HiRes do not have enough statistical power to determine if the GZK suppression is there or not

auger: hybrid detection

AGASA HiRes Auger

Auger energy determination reconstruct S(1000) convert S(1000) to S38 using CIC curve convert S38 to energy using the correlation determined with hybrid data 1019eV

Auger ICRC spectrum 444 17

small scale anisotropy AGASA: 5 doublets + 1 triplet

see also Finley and Westerhoff 2003 AGASA 2pcf point sources (?) DDM, Blasi, Olinto 2005 see also Finley and Westerhoff 2003

B~<10-10 G resol.=2.5º =2.6 m=0 E > 4x1019 eV - 57 events AGASA multiplets B~<10-10 G resol.=2.5º =2.6 m=0 E > 4x1019 eV - 57 events 10-6 Mpc-3 10-5 Mpc-3 10-4 Mpc-3 DDM, Blasi 2004

sources characteristics LCR = 6x1044 erg/yr/Mpc3 (E>1019 eV - from spectrum fits) n0 = 10-5 Mpc-3 (from ssa) Lsrc = 2x1042 erg/s (E>1019 eV) are these ssa for real? the significance of the AGASA result is not clear HiRes doesn’t see them some internal inconsistency

AGASA spectrum discrete sources : 3.2  3.7 DDM, Blasi, Olinto 2005

P~2 10-5 arrival directions DDM, Blasi, Olinto 2005

both the ssa and the spectrum measurement need more statistics to be conclusive and reliable

galactic magnetic field regular + turbulent spiral on the plane exponential decay out of the plane (~1 kpc) ~2 G at Sun position Lmax ~ 100 - 500 pc Bt ~ 0.5 - 2 Breg spectrum: (??) kolmogorov, 5/3 kraichnan, 3/2 sun RL(4x1019eV) = 20 kpc no big deflections except in the disk or in the center

deflections in EGMF - 4x1019eV 110 Mpc Dolag at el. 2003: constrained simulation of the MF in the local universe MF in voids: 10-3-10-1 nG MF in filaments: 0.1-1 nG deflections >1o in less than 2% of sky self-similarity >1o in less than 30% of sky up to 500 Mpc CR astronomy (maybe) possible Sigl et al. 2004: very similar approach, completely different results. Fields in voids higher by 2-4 orders of magnitude. CR astronomy definitely impossible

UHECRs, neutrinos and gamma rays interaction of accelerated protons in the sources or during propagation the neutrino spectrum is unmodified, except for redshift losses gamma rays pile up below the pp threshold on the CMB (~ few 1014eV) universe = calorimeter EGRET diffuse gamma ray flux (MeV - 100 GeV) produces a constraint on neutrino fluxes Lee 1998

CR bound on  from astrophysical sources Waxman & Bahcall 1998 Mannheim, Protheroe, Rachen 2000 EG p: E-2 (thin) max. EG p flux p/ horizon ratio from EG GR bg 1019 - 1021eV EGCR spectrum: energy density of muon neutrinos fraction of energy lost fraction going in neutrinos not valid for top-down sources, optically thick sources…

GZK neutrinos W&B rates per km3 water per year: 0.1-0.2 from neutron decay from neutrons pion-production Engel, Seckel, Stanev 2001 rates per km3 water per year: 0.1-0.2

issues/questions for the future increase statistics above 1020eV: is the GZK feature present? (solve SD-FD discrepancy) increase statistics above 4x1019 eV to identify ssa and possibly determine density of sources measure chemical composition at low energy to determine where the G-XG transition is occurring and at high energy to understand the nature of UHECRs multifrequency observation of the sources