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

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

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

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

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

6. 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

7. 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

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

9. 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

10. 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 5x1019 eV = 1 Gpc
loss 1020 eV = 100 Mpc

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

12. 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

13. 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

14. 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

15. some AGASA spectra
DDM, Blasi, Olinto 2005

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

17. auger: hybrid detection

18. AGASA HiRes Auger

19. 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

20. Auger ICRC spectrum
444 17

21. small scale anisotropy
AGASA: 5 doublets + 1 triplet

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

23. 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

24. 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

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

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

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

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

29. deflections in EGMF - 4x1019eV
110 Mpc
Dolag at el. 2003: constrained simulation of the MF in the local universe
MF in voids: nG MF in filaments: 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

30. 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 GeV) produces a constraint on neutrino fluxes
Lee 1998

31. 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 eV
EGCR spectrum:
energy density of muon neutrinos
fraction of energy lost
fraction going in neutrinos
not valid for top-down sources, optically thick sources…

32. 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:

33. 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