UHECR: PROGRESS AND PROBLEMS

Transcription

1 UHECR: PROGRESS AND PROBLEMS V. Berezinsky INFN, Gran Sasso Science Institute and Laboratori Nazionali del Gran Sasso, Italy

2 PRODUCTION OF HIGH ENERGY PARTICLES UHE particles with energies up to E 20 ev can be produced by acceleration (e.g. shock acceleration, unipolar induction, strong electromagnetic waves) and by cosmological relics in particular by Topological Defects and by Superheavy Dark Matter particles. These particles can be observed as UHECR and neutrinos, in some cases as subdominant component.

3 E max for non-relativistic jets Biermann and Strittmatter 1987, Norman, Melrose, Achtenberg 1995, Ptuskin, Rogovaya, Zirakoshvili, 2013 E max from two conditions: E max = ZeBR s (Hillas criterion) and B 2 /8π = ω part or B 2 /8π L/πRscβ 2 (equipartition), results in E max Ze(8L/c) 1/ ZL 1/2 45 ev (1) for β 1. Eq. (1) does not depend on r sh and R s. Problem: At Γ j < 4 jets are short, and HE protons are absorbed due to pγ interaction.

4 Fanaroff-Riley I and II radio-galaxies

5 ACCELERATION IN RELATIVISTIC SHOCKS looks very promising because at reflection a particle obtains E Γ 2 sh E i

6 Illustrative picture Problems *

7 Recent progress Based on PIC simulations (Spitkovsky 2008, Sironi and Spitkovsky 2011) the small-scale microturbulence produced due to self-generated streaming instability results in repeating scattering between upstream and downstream (Fermi process) and in acceleration of particles (see Lemoine and Pelletier , Bykov et al 2012, Reville and Bell 2014). The basic features are as follows: Streaming instability is produced by interaction of reflected flow of gas with the direct flow. Repeating transition between upstream and downstream is caused by scattering on small-scale microturbulence. Particles are confined to small θ 1/Γ sh. The scale of microturbulence is given by λ c/ω pp, where ω pp = 4πne 2 /γm p is relativistic plasma frequency. In the recent work by Reville and Bell (2014) the new element was included, the growth-rate time of instability. This rate is found to be very low and it limits strongly E max.

8 B. Reville and A.R. Bell 2014 The calculated growth-rates (of plasma instability) have insufficient time to modify the scattering, the acceleration to higher energies is ruled out. E max ( ) 2 ( ) Γsh λd ( σd ) ( σu ) 1/2 PeV 0 c/ω pp 2 8 Ultra-relativistic shocks are disfavoured as sources of high energy particles, in general... this paper is not the first to suggest that GRBs are not the sources of UHECRs, but we gone one step further..

9 TOPOLOGICAL DEFECTS Symmetry breaking in early universe results in phase transitions (D. Kirzhnitz 1972), accompanied by TDs (T. Kibble). Their common feature is production of HE particles. Ordinary and superconducting strings Produced at U(1) symmetry breaking. Particles are massless inside the string and massive outside. Loop oscillates with periodically produced cusp (v = c) and with large Lorentz factors, e.g. above Γ, at nearby points. Particles escaping from cusp segment have E max Γ c η, Particles are emitted as jets with θ 1/Γ c. In a wide class of particle physics strings are superconducting (Witten 1985) UHE neutrino jets from superconducting strings V.B., K.Olum, E.Sabancilar and A.Vilenkin 2009 Electric current is generated in magnetic fields (B, f B ), dominated by clusters. Clusters of galaxies dominate. Lorentz factor of cusp Γ c η 9 GeV, E max 21 GeV. Diffuse neutrino flux : E 2 J ν (E) = 2 8 i c B 6 f 3 GeVcm 2 s 1

10 UHE NEUTRINOS FROM ORDINARY STRINGS. 1. Ordinary strings with EW Higgs condensate. Vachaspati 20 Interaction of EW Higgs φ with the string field Φ ( κ is coupling constant): S int = κ d 4 x(φ + Φ η 2 )φ + φ After GUT symmetry breaking ( < Φ >= η ): S int = κη d 2 σ γ φ, where d 2 σ is string world-sheet space, γ ab is the world-sheet metric. The higgses are emitted through the cusp. 1. UHE neutrinos emitted from ordinary strings via dilatons and moduli. VB, Sabancilar, Vilenkin, 2011 following Damour and Vilenkin S int = ( 4πα/M Pl ) d 4 x φ T ν ν, T ν ν (x) = 2η 2 d 2 σ γ δ 4 (x α x α (σ)) is the trace of energy-momentum tensor of string. Dilatons and moduli are produced as radiation quanta from the cusp. In terms of the Fourier momenta k : dn(k) = α 2 Gη 4 l 2/3 k 7/3 dk.

11 UHECR: propagation, signatures and mass composition

12 Total CR spectrum Flux (m 2 sr s GeV) Knee (1 particle per m 2 -year) nd knee Ankle (1 particle per km 2 -year) Energy (ev)

13 Spectrum and Features

14 Signatures of particle propagation through CMB and EBL CMB + EBL -5-6 Iron A=56, z=0 τ -1 A -1 de/dt(e), yr -1 E -9 - total adiabatic y β A pair EBL e e pion production - H E, ev Γ E eq1 = ev, E eq2 = ev Pair-production dip and GZK cutoff. Nuclei photo-dissociation: GR cutoff τ ebl A (Γ c) = τ cmb A (Γ c)

15 UHE protons INTERACTION SIGNATURES AND MODEL-DEPENDENT SIGNATURES We want to see observational signatures of interaction, but in our calculations model-dependent quantities also appear, such as distances between sources, their cosmological evolution, modes of propagation (from rectilinear to diffusion), local source overdensity or deficit etc. Energy spectrum in terms of modification factor characterizes well the interaction signatures.

16 MODIFICATION FACTOR η(e) = J p(e) (E) J unm p where Jp unm (E) = KE γ g includes only adiabatic energy losses. Since many physical phenomena in numerator and denominator compensate or cancel each other, dip in terms of modification factor is less model-dependent than J p (E). It depends very weakly on: γ g and E max, modes of propagation (rect or diff), large-scale source inhomogeneity, source separation within 1-50 Mpc, local source overdensity or deficit,.. It is modified by presence of nuclei (> 15%). Experimental modification factor: η exp (E) = J obs (E)/KE γ g. η(e) γ g = E, ev 21 - e + e total 22

17 Comparison of pair-production dip with observations 0 0 modification factor -1 Akeno-AGASA η ee modification factor -1 Yakutsk η ee -2 γ g =2.7 η total -2 γ g =2.7 η total E, ev E, ev modification factor HiRes I - HiRes II γ g =2.7 η ee η total modification factor TA MD TA SD γ =2.6 g η ee η total E, ev E, ev 20 21

18 GZK CUTOFF IN HiRes DIFFERENTIAL SPECTRUM 0 modification factor -1 HiRes I - HiRes II η ee -2 γ g =2.7 η total E, ev

19 GZK CUTOFF IN HiRes INTEGRAL SPECTRUM J(>E)/KE γ log (E) (ev) E 1/2 in HiRes integral spectrum confirms that steepening in the differential spectrum is the GZK cutoff: E meas 1/2 = 19.73±0.07 ev cf E theor 1/2 = ev

20 DIRECT MEASUREMENTS OF MASS COMPOSITION is a necessary component of consistent picture

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22 MASS COMPOSITION: HIRES (top) vs AUGER (bottom)

23 Interpretation of Auger spectrum and mass composition Aloisio, V.B., Blasi (2013), see also Taylor, Ahlers, Aharonian (2012). γg = 1.0, Emax = 5Z EeV γg (p, He) = 2.7 E 3 J(E) (ev 2 m -2 s -1 sr -1 ) γ g =1.0, E max =5Zx 18 ev p He CNO MgAlSi Fe E 3 J(E) (ev 2 m -2 s -1 sr -1 ) γ g (A>4)=1.0, γ g (p,he)=2.7 E max =3Zx 19 ev p He CNO MgAlSi Fe E (ev) E (ev) <X max > (g/cm 2 ) EPOS Sibyll QGSJet1 QGSJet2 σ(x max ) (g/cm 2 ) E (ev) E (ev)

24 0 * * - * ) " # Impact of KASCADE-Grande experiment Small m 2 array with scintillation and muon detectors. p+he component is separated by muon content with properties: p+he component at EeV separated as electron-rich using special event criteria, 6300 events. extragalactic, otherwise anisotropy at E 1 EeV. flat spectrum γ = 2.79 ± 0.08, cf γ = 3.24 ± 0.08 for total. ' 1. %.,/. + $,+ $&% ' ( "! C 7 j VWYXZYW\[Y]J^ _` abccd HJI KLM&N OLO&N HSI KLTU OLOK HJI PLK&N OLO&N 7 h fecg 7 i fecg HJI PLK&Q OLOR HSI PLK&Q OLO&N HSI KLTM OLOR CB CBD E CG CGCD E F 8:9<;,=?>A@

25 CONCLUSIONS UHECR are characterised by high E max (the highest energy observed is 3 20 ev) and by propagation signatures in energy spectrum. The propagation signatures for protons are pair-production dip (due to p+γ cmb p+e + +e ) and GZK cutoff (due to p+γ cmb N + π). The propagation signature for nuclei is GR cutoff with Γ c (3 4) 9 for all nuclei, and E GR AΓ c m N (3 4)A 18 ev, if E GR < Emax. acc HiRes and TA observed proton dominance in the direct measurements of the mass composition and signatures of proton interaction with CMB: pair-production dip and GZK cutoff in differential and integral spectra.

26 Auger reports the nuclei composition steadily heavier with increasing energy. The models which explain simultaneously the Auger energy spectrum, X max (E) and RMS (dispersion) must have very flat generation spectrum γ g < 1.6 and additional EeV proton+he component with steep spectrum. The main problem of UHECR at present is contradiction between HiRes/TA and PAO data on mass composition at E > (3 5) EeV. From Auger data there must be the sources at distance Mpc (Taylor, Ahlers, Aharonian 2011) and the detection of these sources in the future experiments may solve the UHECR puzzle.