ultra high energycosmic rays:

theoretical aspects

Daniel De MarcoBartol Research InstituteUniversity of Delaware

2

plan

observations & open issues

origin of UHECRspropagation: the GZK

featuresmall scale anisotropiesUHECRs, -rays and s

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indirect observation (EAS)direct observation

(1 particle per km2--century)

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indirect observation (EAS)direct observation

(1 particle per km2--century)many joules in

one particleUHECR

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UHECRs: observations

AGASAHiResAuger

spectrum

arrival dirs. low energy

composition

Ostapchenko, Heck 2005

arrival directions high energy AGASA

AGASA

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AGASAHiResAuger

spectrum

composition

Ostapchenko, Heck 2005

UHECRs: observations

arrival dirs. low energy

arrival directions high energy AGASA

AGASA

two (separate) issuesproductio

nfor astrophysical accelerators it is challenging to accelerate particles to such high energies.

propagationGZK feature in the energy spectrum due to the interactions with the photons of the CMB

end of the CR spectrum at some

high energy

strong flux suppression around 5

x 1019eV

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origin of UHECRsbottom-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

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hillas plot Emax ≤ Ze B L

Olinto 2000

Hillas 1984

accounting for energy losses the situation is even more difficult

lines: 1020 eV

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origin of UHECRsbottom-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

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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%)GZK suppression:

loss length @ 5x1019 eV = 1 Gpcloss length @ 1020 eV = 100 Mpc

loss lengths

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GZK feature: single sourcemodification factor: observed spectrum / injection spectrum

bump

suppression

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similar conclusions for nuclei and gamma rays: CRs can not reach us at

UHE if theyare 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

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AGASA & HiRes

a factor 2 in

the flux

HiRes: GZK

AGASA: no GZK

AGASA claims noGZK at 4HiRes claims GZK at 4

actual discrepancies

more like~3 and ~2

DDM, Blasi, Olinto 2003, 2005

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systematic errors (?)AGASA -15%

HiRes +15%agreement

at low energy

less disagreement at

high energyhow much??

~2DDM, Blasi, Olinto 2003, 2005DDM, Stanev 2005

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som

e AG

ASA

spec

tra

DDM, Blasi, Olinto 2005

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both AGASA and HiRes do not have enough

statistical power to determine if the GZK

suppression is there or not

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auger:hybrid

detection

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AGASAHiResAuger

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Auger energy determination

1019eV

•reconstruct S(1000)•convert S(1000) to S38 using CIC curve

•convert S38 to energy using the correlation determined with hybrid data

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Auger ICRC spectrum

444

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small scale anisotropy

AGASA: 5 doublets + 1 triplet

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AGASA 2pcf point sources (?)

see also Finley and Westerhoff 2003DDM, Blasi, Olinto 2005

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AGASA multipletsB~<10-10 G resol.=2.5º

=2.6 m=0E > 4x1019 eV - 57 events

10-6 Mpc-3

10-5 Mpc-3 10-4 Mpc-3

DDM, Blasi 2004

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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

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P: 6 10-4 2 10-4

: 3.2 3.7

AGASA spectrumdiscrete sources

DDM, Blasi, Olinto 2005

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arriv

al

dire

ctio

nsP~2 10-5

DDM

, Bla

si, O

linto

200

5

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both the ssa and the spectrum measurement

need more statistics to beconclusive and reliable

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galactic magnetic fieldregular + 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, 5/3kraichnan, 3/2

RL(4x1019eV) = 20 kpcno big deflections except in the disk or in the center

sun

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deflections in EGMF - 4x1019eV 110 Mpc

deflections>1o in less than 2% of

sky• self-similarity

>1o in less than 30% of sky up to 500 Mpc

Dolag at el. 2003: constrained simulation of the MF in the local universeMF in voids: 10-3-10-1 nGMF in filaments: 0.1-1 nG

Sigl et al. 2004: very similar approach, completely different results. Fields in voids higher by 2-4 orders of magnitude.

CR astronomy (maybe) possible

CR astronomy definitely impossible

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UHECRs, neutrinos and gamma raysinteraction 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

Lee 1998

EGRET diffuse gamma ray flux(MeV - 100 GeV) produces a constraint on neutrino fluxes

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Mannheim, Protheroe, Rachen 2000

EG p: E-2(thin)

max.EG pflux

p/ horizon ratio

from EG GR bg

CR bound on from astrophysical sources

Waxman & Bahcall 1998

EGCR spectrum:1019 - 1021eV

fraction of energy lost

fraction going in neutrinos

energy density of muon neutrinos

not valid for top-down sources,optically thick sources…

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GZK neutrinos

rates per km3 water per year: 0.1-0.2

W&B

from neutron decay from neutronspion-production

Engel, Seckel, Stanev 2001

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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