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Ultra-high Energy Cosmic Rays: Challenges and Opportunities

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  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 • UHECRs beyond the GZK cutoff • UHECRs I: beyond standard lore? • Lorentz Invariance • TDs: fossils of the GU era • Z-bursts • Others • UHECRs II:  or strangelets? • Conclusions “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

  3. Introduction: CRs as HEP Frontier • 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 “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

  4. Introduction: CRs as HEP Frontier UHECRs: >~1019eV Within the Galaxy The highest! “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

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

  6. UHECRs beyond the GZK cutoff • GZK cutoff: estimations Ep ~ 1019 eV,  ~ Ep/1GeV ~ 1010 ECB ~ 3 K ~ 10-4 eV Electron rest frame E’CB ~  ECB ~ MeV Greisen PRL (1966); Zatsepin & Kuzmin JETP (1966) “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

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

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

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

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

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

  12. UHECRs I: beyond standard lore? • 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 boosts “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

  13. UHECRs I: beyond standard lore? • Quantum space-time foam Heisenberg relation Mcl ~ l ~ /(Mc) Schwartzschild radius Rs~ GM/c2 Virtual particles contribute to curvature significantly when Rs~ l Plank mass: Mpl = ( c/G)1/2 = 2.1810-5 g = 1.221016 TeV “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

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

  15. UHECRs I: beyond standard lore? • 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. “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

  16. UHECRs I: beyond standard lore? • 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 “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

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

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

  19. UHECRs I: beyond standard lore? • 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 “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

  20. UHECRs I: beyond standard lore? • Z-bursts Weiler, T. 1999, Astropart. Phys., 11 303 • Larger cross section of resonant Z0production by - occurs for • E = mz2/(2m) ~ 41021/(m /eV) eV [mz~ 91 GeV, m~ (0.05-8.4) eV; ~10-32cm2] • 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 “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

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

  22. SUMMARY • Introduction: CRs as HEP Frontier • UHECRs beyond the GZK cutoff • UHECRs I: beyond standard lore? • Lorentz Invariance • TDs: fossils of the GU era • Z-bursts • Others • UHECRs II:  or strangelets? • 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 Why? • The Plank scale • 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 withExtra spatial Demensions (EDs)might be responsible for the hierarchy between Mpl and MEW. • The fundamental gravity scale with n EDs “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

  26. Why TeV-scale BHs • What if M* ~ MEW ~ TeV ... • 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 ... • When the c.m. energy Ecm=(2c2mqE)1/2 > M*, A TeV-scale black hole forms, with an interaction cross section BH ~ rs2 UHE E rs . Quark “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

  29. The interaction of UHE with ... • Gravity interaction dominates if E> ~1015eV Increase the cross section! Economic ideal: UHE Feng-Shapere PRL 88 (2002) 021303 “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

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

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

  32. The interaction of UHE with ... • What is a Bare Strange Star? • crusted • bare “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 ... • Two steps of collapse: • 1st: “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

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

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

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

  38. UHECRs: Strangelets? • What is the astrophysicalorigin of strangelets? • in early cosmology? • after supernova exploration! • Acceleration in induced electric field ~ 1017/P10eV • 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 • UHECRs beyond the GZK cutoff • UHECRs I: beyond standard lore? • Lorentz Invariance • TDs: fossils of the GU era • Z-bursts • Others • UHECRs II:  or strangelets? • Conclusions “UHECRs” http://vega.bac.pku.edu.cn/rxxu R.X. Xu

  40. Conclusions • The cosmic ray study at the highest energy __(UHECRs) is again the frontier of Part. Ph. • UHECRs could potentially open a window __to probe new physics beyond the SM • Strangelets may be candidates of UHECRs, __and may evencontribute a significant part __of cosmic rays with energy < 1019 eV! “UHECRs: Strangelets?” http://vega.bac.pku.edu.cn/rxxu R.X. Xu