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Neutrino Physics III

This document outlines the key points discussed during the Neutrino Physics III session by Hitoshi Murayama at the Taiwan Spring School on March 28, 2002. Topics include the LSND anomaly, neutrino mass implications, the existence of matter, and models of flavor oscillation. It highlights the challenges in accommodating the LSND evidence within current neutrino models and discusses potential new particles, the significance of sterile neutrinos, and implications for upcoming experiments like Mini-BooNE and SNO. The talk concludes with considerations about the enigma of baryon asymmetry in the universe.

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Neutrino Physics III

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  1. Neutrino Physics III Hitoshi Murayama Taiwan Spring School March 28, 2002

  2. 中性微子物理（三） 村山　斉 台湾春期学校 二千二年三月二十八日

  3. Outline • LSND • Implications of Neutrino Mass • Why do we exist? • Models of flavor • Conclusions

  4. LSND

  5. Excess positron events over calculated BG 3.3s Signal

  6. LSND unconfirmed Neutrino beam from Fermilab booster Settles the issue of LSND evidence Start data taking later this year Mini-BooNE

  7. SN1987A neutrino burstdoesn’t like LSND • Kamiokande’s 11 events: • 1st event is forward may well be ne from deleptonization burst (p e- n ne to become neutron star) • Later events most likely ne • LSND parameters cause complete MSW conversion of nenm if light side (ne lighter) nenm if dark side (ne heavier) • Either mass spectrum disfavored _ _ _ HM, Yanagida

  8. SN1987A neutrino burstdoesn’t like LSND HM, Yanagida

  9. LSND, atmospheric and solar neutrino oscillation signals Dm2LSND ~ eV2 Dm2atm ~ 310–3eV2 Dm2solar < 10–3eV2  Can’t be accommodated with 3 neutrinos  Need a sterile neutrino New type of neutrino with no weak interaction 3+1 or 2+2 spectrum? Sterile Neutrino

  10. Sterile Neutrino getting tight • 3+1 spectrum: sin22qLSND=4|U4e|2|U4m|2 • |U4m|2 can’t be big because of CDHS, SK U/D • |U4e|2 can’t be big because of Bugey • Marginally allowed (90% excl. vs 99% allw’d) • 2+2 spectrum: past fits preferred • Atmospheric mostly nmnt • Solar mostly nens(or vice versa) • Now solar sterile getting tight (Barger et al, Giunti et al, Gonzalez-Garcia et al, Strumia)

  11. Global fit to four-neutrino oscillation Solar, Atmospheric, LSND (Gonzalez-Garcia, Maltoni, Peña-Garay@EPS01) One can still find a reasonable fit with 2+2  Disfavored at 90-99% CL Not Quite Excluded Yet… ne nt nm ns nens nmnt

  12. LSND evidence: anti-neutrinos Solar evidence: neutrinos If neutrinos and anti-neutrinos have different mass spectra, atmos-pheric, solar, LSND accommodated without a sterile neutrino (HM, Yanagida) CPT Violation?“A desperate remedy…”

  13. CPT Theorem • Based on three assumptions: • Locality • Lorentz invariance • Hermiticity of Hamiltonian • Violation of any one of them: big impact on fundamental physics • Neutrino mass: tiny effect from high-scale physics • Non-commutative geometry? (HM, Yanagida) • Brane world? (Barenboim, Borissov, Lykken, Smirnov)

  14. Implications on Experiments • Mini-BooNE experiment will not see oscillation in neutrino mode, but will in anti-neutrino mode • SNO, Borexino establish LMA, while KamLAND will not see oscillation • Katrin may see endpoint distortion  We’ll see!

  15. Maybe even more surprisesin neutrinos!

  16. Implications of Neutrino Mass

  17. Mass Spectrum What do we do now?

  18. (1) Dirac Neutrinos: There are new particles, right-handed neutrinos, after all Why haven’t we seen them? Right-handed neutrino must be very very weakly coupled Why? Two ways to go

  19. Extra Dimensions • Right-handed neutrinos SM gauge singlet • Can propagate in the “bulk” • Makes neutrino mass small (Arkani-Hamed, Dimopoulos, Dvali, March-Russell; Dienes, Dudas, Gherghetta; Grossman, Neubert) • mn ~ 1/R if one extra dim  R~10mm • An infinite tower of sterile neutrinos • Need also inter-generational mixing now

  20. (2) Majorana Neutrinos: There are no new light particles Why if I pass a neutrino and look back? Must be right-handed anti-neutrinos No fundamental distinction between neutrinos and anti-neutrinos! Two ways to go

  21. Seesaw Mechanism • Why is neutrino mass so small? • Need right-handed neutrinos to generate neutrino mass , but nR SM neutral To obtain m3~(Dm2atm)1/2, mD~mt, M3~1015GeV (GUT!)

  22. electromagnetic, weak, and strong forces have very different strengths But their strengths become the same at 1016 GeV if supersymmetry To obtain m3~(Dm2atm)1/2, mD~mt  M3~1015GeV! Grand Unification M3 Dimopoulos, Raby, Wilczek Neutrino mass may be probing unification: Einstein’s dream

  23. Matter Anti-matter AsymmetryWhy do we exist?

  24. Big-Bang NucleosynthesisCosmic Microwave Background (Thuan, Izatov) (Burles, Nollett, Turner)

  25. Baryon AsymmetryEarly Universe 10,000,000,001 10,000,000,000 They basically have all annihilated away except a tiny difference between them

  26. Baryon AsymmetryCurrent Universe us 1 They basically have all annihilated away except a tiny difference between them

  27. Sakharov’s Conditionsfor Baryogenesis • Necessary requirements for baryogenesis: • Baryon number violation • CP violation • Non-equilibrium  G(DB>0) > G(DB<0) • Possible new consequences in • Proton decay • CP violation

  28. Original GUT Baryogenesis • GUT necessarily breaks B. • A GUT-scale particle X decays out-of-equilibrium with direct CP violation • Now direct CP violation observed: e’! • But keeps B–L0 “anomaly washout” • Also monopole problem

  29. Actually, SM violates B (but not B–L). In Early Universe (T > 200GeV), W/Z are massless and fluctuate in W/Z plasma Energy levels for left-handed quarks/leptons fluctuate correspon-dingly DL=DQ=DQ=DQ=DB=1  B=L=0 Anomaly washout

  30. Two Main Directions • BL0 gets washed out at T>TEW~174GeV • Electroweak Baryogenesis(Kuzmin, Rubakov, Shaposhnikov) • Start with B=L=0 • First-order phase transition  non-equilibrium • Try to create BL0 • Leptogenesis(Fukugita, Yanagida) • Create L0 somehow from L-violation • Anomaly partially converts L to B

  31. Leptogenesis

  32. Leptogenesis • You generate Lepton Asymmetry first. • Generate L from the direct CP violation in right-handed neutrino decay • Two generations enough for CP violation because of Majorana nature (choose 1 & 3) • L gets converted to B via EW anomaly  More matter than anti-matter  We have survived “The Great Annihilation”

  33. Does Leptogenesis Work? • Much more details worked out (Buchmüller, Plümacher; Pilaftsis) • ~1010 GeV nR OK • Some tension with supersymmetry because of unwanted gravitino overproduction • Ways around: coherent oscillation of right-handed sneutrino (HM, Yanagida+Hamaguchi)

  34. Some tension with supersymmetry: unwanted gravitino overproduction gravitino decay dissociates light nuclei destroys the success of Big-Bang Nucleosynthesis Need TRH<109 GeV Does Leptogenesis Work? • (Kawasaki, Kohri, Moroi)

  35. Coherent oscillation of right-handed sneutrino (Bose-Einstein condensate) (HM, Yanagida+Hamaguchi) Inflation ends with a large sneutrino amplitude Starts oscillation dominates the Universe Its decay produces asymmetry Consistent with observed oscillation pattern isocurvature fluctuation ~10-7 Leptogenesis Works!

  36. Can we prove it experimentally? • We studied this question at Snowmass2001 (Ellis, Gavela, Kayser, HM, Chang) • Unfortunately, no: it is difficult to reconstruct relevant CP-violating phases from neutrino data • But: we will probably believe it if • 0nbb found • CP violation found in neutrino oscillation • EW baryogenesis ruled out Archeological evidences

  37. Conclusions • Neutrinos are weird • Strong evidence for neutrino mass • Small but finite neutrino mass: • Need drastic ideas to understand it • If Majorana, neutrino mass may be responsible for our existence • A lot more to learn in the next few years

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