1. Ultra-high Energy Cosmic Rays: Challenges and Opportunities Renxin Xu ( 徐仁新 ) School of Physics, Peking University Talk presented at the Conference of 基于羊八井平台的交叉学科研究 April 6, 2004, CCAST “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

2. SUMMARY Introduction: CRs as HEP Frontier Introduction: CRs as HEP Frontier UHECRs beyond the GZK cutoff UHECRs beyond the GZK cutoff UHECRs I: beyond standard lore? UHECRs I: beyond standard lore?  Lorentz Invariance  TDs: fossils of the GU era  Z-bursts  Others UHECRs II: or strangelets? UHECRs II: or strangelets? Conclusions Conclusions “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

3. Introduction: CRs as HEP Frontier “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu  The higher the particle energy attained, the smaller __the scale of physics which can be probed.  Cosmic rays vs. Particle physics 1937 (Anderson & Neddermeyer):  1947(Power):  1947( Rochester & Butler): strange part.  0, K,...  Cosmic rays vs. Astrophysics Generally, astrophysics studies “cosmic rays” Astrophysics offers extreme environments

4. Introduction: CRs as HEP Frontier “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu UHECRs: >~10 19 eV The highest! Within the Galaxy

5. SUMMARY Introduction: CRs as HEP Frontier Introduction: CRs as HEP Frontier UHECRs beyond the GZK cutoff UHECRs beyond the GZK cutoff UHECRs I: beyond standard lore? UHECRs I: beyond standard lore?  Lorentz Invariance  TDs: fossils of the GU era  Z-bursts  Others UHECRs II: or strangelets? UHECRs II: or strangelets? Conclusions Conclusions “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

6. UHECRs beyond the GZK cutoff “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu u GZK cutoff: estimations E p ~ 10 19 eV,  ~ E p /1GeV ~ 10 10 E CB ~ 3 K ~ 10 -4 eV Electron rest frame E’ CB ~  E CB ~ MeV Greisen PRL (1966); Zatsepin & Kuzmin JETP (1966)

7. UHECRs beyond the GZK cutoff “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu u GZK cutoff: in theory Loss length for Proton with pair and photopion productions Scale of the Galaxy

8. u The GZK cutoff with threshold u Other particles Photon, Iron UHECRs beyond the GZK cutoff “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

9. UHECRs beyond the GZK cutoff “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu u No clear GZK cutoff observed Stecker 2003

10. UHECRs beyond the GZK cutoff “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu u Prediction vs. observation Stecker 2003

11. SUMMARY Introduction: CRs as HEP Frontier Introduction: CRs as HEP Frontier UHECRs beyond the GZK cutoff UHECRs beyond the GZK cutoff UHECRs I: beyond standard lore? UHECRs I: beyond standard lore?  Lorentz Invariance  TDs: fossils of the GU era  Z-bursts  Others UHECRs II: or strangelets? UHECRs II: or strangelets? Conclusions Conclusions “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

12. UHECRs I: beyond standard lore? “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu  Lorentz symmetry (invariance) Essence of special relativity:  no absolute reference frame Poincare group = T(4) + O(1, 3) Lorentz group O(1, 3) = 3R + 3R´  light propagates at a maximum constant speed c in all reference boos ts

13. UHECRs I: beyond standard lore? “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu Mc  l ~  l ~ /(Mc)  Quantum space-time foam Heisenberg relation Schwartzschild radius R s ~ GM/c 2 Virtual particles contribute to curvature significantly when R s ~ l Plank mass: M pl = ( c/G) 1/2 = 2.18  10 -5 g = 1.22  10 16 TeV

14. UHECRs I: beyond standard lore? “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu  Lorentz violation? (Jacobson, T., Liberati, S. & Mattingly, D. Nature 424, 1019–1021, 2003) Photons: Electrons:  opposites for L or R Modified dispersion relations?

15. UHECRs I: beyond standard lore? “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu u LV of UHECRs? Coleman and Glashow ( 1999, PRD59, 116008 ): show that only a very tiny amount of LI symmetry breaking is required to avoid the GZK effect by suppressing photomeson interactions between ultrahigh energy protons and the CBR.

16. UHECRs I: beyond standard lore? “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu u TD: fossils of the GU era  Topological defects (TD) may be produced at the post- inflation stage of the early Universe: e.g., monopoles, cosmic strings, monopoles connected by strings, etc.  Superheavy particles (called X-particles ) could be emitted during TD evolution; e.g., annihilation of monopole- antimonopole.  X-particles could be: superheavy Higgs particles gauge bosons massive SUSY particles

17. UHECRs I: beyond standard lore? “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu u TD: fossils of the GU era Fragmentation of X-particles

18. UHECRs I: beyond standard lore? “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu u TD: fossils of the GU era Berezinsky et al. PRD58 103515 (1998)

19. UHECRs I: beyond standard lore? “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu u Z-bursts Weakly interacting particles such as neutrinos will have no difficulty in propagating over extragalactic distances Difficulty in the neutrino hypothesis: The fly’s Eye event occurred high in the atmosphere, whereas the expected event rate for early development of neutrino-induced air shower is down from that of an electromagnetic or hadronic interaction by six orders of magnitude. But

20. UHECRs I: beyond standard lore? “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu u Z-bursts Weiler, T. 1999, Astropart. Phys., 11 303  Larger cross section of resonant Z 0 production by - occurs for E = m z 2 /(2m ) ~ 4  10 21 /(m /eV) eV [m z ~ 91 GeV, m ~ (0.05-8.4) eV;  ~10 -32 cm 2 ]  Clustering of the 1.9 K cosmic background neutrinos  ~70% of interactions  Z-burst : photons (~30) + nucleons (~2.7)  These photons and nucleons produced within our supergalactic halo propagate to earth and initiate super- GZK air showers

21. UHECRs I: beyond standard lore? “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu u Others  Ultraheavy dark matter particles: ‘ wimpzillas ’  Other new particles: e.g., neutral hadrons containing a light gluino

22. SUMMARY Introduction: CRs as HEP Frontier Introduction: CRs as HEP Frontier UHECRs beyond the GZK cutoff UHECRs beyond the GZK cutoff UHECRs I: beyond standard lore? UHECRs I: beyond standard lore?  Lorentz Invariance  TDs: fossils of the GU era  Z-bursts  Others UHECRs II: or strangelets? UHECRs II: or strangelets? Conclusions Conclusions “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

23. Black holes in our Universe  Supermassive black holes  Stellar black holes  Primordial black holes TeV-scale black holes? “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

24. Why TeV-scale BHs  The hierarchy problem and EDs u The Plank scale u But, the electroweak scale “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

25. Why TeV-scale BHs  Arkani-Hamed, Dimopoulos & Dvali 1998, Phys. Lett. B429 263 The geometry with Extra spatial Demensions (EDs) might be responsible for the hierarchy between M pl and M EW. u The fundamental gravity scale with n EDs “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

26. u What if M * ~ M EW ~ TeV... Why TeV-scale BHs  Implication I: Large EDs with Radius R Observation? “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

27. Why TeV-scale BHs  Implication II: TeV-scale mini black holes “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

28. The interaction of UHE with... u When the c.m. energy E cm =(2c 2 m q E ) 1/2 > M *, A TeV-scale black hole forms, with an interaction cross section  BH ~  r s 2 E UHE. Quark rsrs “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

29. The interaction of UHE with... u Gravity interaction dominates if E > ~10 15 eV Feng-Shapere PRL 88 (2002) 021303 “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu Increase the cross section! Economic ideal: UHE

30. The interaction of UHE with... u The Schwartzchild radius, with n EDs u The Hawking radiation, with n EDs “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

31. The interaction of UHE with... u UHE bombarding a nucleon:  in relativistic heavy ion colliders  in atmospheric detectors u UHE bombarding a Bare SS:  Collapse to a stellar black hole? “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

32. u What is a Bare Strange Star? o crusted o bare The interaction of UHE with... “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

33. The interaction of UHE with...  Possible evidence for bare strange stars  Drifting subpulses in radio emission  No atomic spectrum in X-ray emission  Extreme super-Eddington emission in SGRs  Glitch and free-precession of radio pulsars For reviews, see: Xu (astro-ph/0211563) Xu (astro-ph/0310050) “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

34. The interaction of UHE with... u Two steps of collapse: à 1st: “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

35. The interaction of UHE with... à 2nd: “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

36. The interaction of UHE with... à BSSs as probe to the flux of UHE Exist of BSS “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

37. ML03 UHECRs: Strangelets? u What is Strangelet?=> A lump of strange matter u Advantages if UHECRs are strangelets:  Larger mass Byond GZK cutoff  Higher electricity Easier to accelerate  Not point-like No collapse to BHs “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

38. UHECRs: Strangelets? u What is the astrophysical origin of strangelets?  in early cosmology?  after supernova exploration! Acceleration in induced electric field ~ 10 17 /P 10 eV strangelets left behind in debris disk Planets observed around radio pulsars? Soft  -ray Repeater: burst via collision? “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

39. SUMMARY Introduction: CRs as HEP Frontier Introduction: CRs as HEP Frontier UHECRs beyond the GZK cutoff UHECRs beyond the GZK cutoff UHECRs I: beyond standard lore? UHECRs I: beyond standard lore?  Lorentz Invariance  TDs: fossils of the GU era  Z-bursts  Others UHECRs II: or strangelets? UHECRs II: or strangelets? Conclusions Conclusions “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

40. “UHECRs: Strangelets?” http://vega.bac.pku.edu.cn/rxxu R.X. Xu Conclusions u The cosmic ray study at the highest energy __(UHECRs) is again the frontier of Part. Ph. u UHECRs could potentially open a window __to probe new physics beyond the SM u Strangelets may be candidates of UHECRs, __and may even contribute a significant part __of cosmic rays with energy < 10 19 eV!