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Origin of Neutrino Mass

Origin of Neutrino Mass. Hitoshi Murayama (UC Berkeley) Neutrinos in Cosmology, in Astro, Particle and Nuclear Physics Erice, 17th September, 2005. Outline. Introduction Implications of Neutrino Mass Seven Questions Why do we exist? Models of Flavor Conclusion. Introduction.

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Origin of Neutrino Mass

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  1. Origin of Neutrino Mass Hitoshi Murayama (UC Berkeley) Neutrinos in Cosmology, in Astro, Particle and Nuclear Physics Erice, 17th September, 2005

  2. Outline • Introduction • Implications of Neutrino Mass • Seven Questions • Why do we exist? • Models of Flavor • Conclusion Erice 2005

  3. Introduction

  4. The Question • So much activity on neutrino mass already. Why are we doing this? Window to (way) high energy scales beyond the Standard Model! Erice 2005

  5. Why Beyond the Standard Model • Standard Model is sooooo successful. But none of us are satisfied with the SM. Why? • Because it leaves so many great questions unanswered  Drive to go beyond the Standard Model • Two ways: • Go to high energies • Study rare, tiny effects  Erice 2005

  6. Rare Effects from High-Energies • Effects of physics beyond the SM as effective operators • Can be classified systematically (Weinberg) Erice 2005

  7. Unique Role of Neutrino Mass • Lowest order effect of physics at short distances • Tiny effect (mn/En)2~(eV/GeV)2=10–18! • Inteferometry (i.e., Michaelson-Morley)! • Need coherent source • Need interference (i.e., large mixing angles) • Need long baseline Nature was kind to provide all of them! • “neutrino interferometry” (a.k.a. neutrino oscillation) a unique tool to study physics at very high scales Erice 2005

  8. Ubiquitous Neutrinos Erice 2005

  9. Sun as a neutrino source SuperK image of the Sun Erice 2005

  10. We don’t get enough We need survival probabilities of 8B: ~1/3 7Be: <1/3 pp: ~2/3 Can we get three numbers correctly with two parameters? Erice 2005

  11. Year of Neutrino: 2002 March 2002 April 2002 with SNO Dec 2002 with KamLAND Erice 2005

  12. Solar Neutrino Problem Finally Solved After 35 Years!

  13. Historic Era in Neutrino Physics We learned: • Atmospheric nms are lost. P=4.2 10–26(SK) • converted most likely to nt • Solar ne is converted to either nm or nt(SNO) • Reactor anti-ne disappear and reappear (KamLAND) • Only the LMA solution left for solar neutrinos • Neutrinos have tiny but finite mass the first evidence for incompleteness of Minimal Standard Model Erice 2005

  14. CP Violation • Possible only if: • Dm122, s12 large enough (LMA) • q13 large enough • Can we see CP violation? Erice 2005

  15. Typical Theorists’ View ca. 1990 • Solar neutrino solution must be small angle MSW solution because it’s cute • Natural scale for Dm223 ~ 10–100 eV2 because it is cosmologically interesting • Angle q23 must be ~ Vcb =0.04 • Atmospheric neutrino anomaly must go away because it needs a large angle Wrong! Wrong! Wrong! Wrong! Erice 2005

  16. Implications of Neutrino Mass

  17. Neutrinos are Left-handed Erice 2005

  18. Neutrinos must be Massless • All neutrinos left-handed  massless • If they have mass, can’t go at speed of light. • Now neutrino right-handed??  contradiction  can’t be massive Erice 2005

  19. Standard Model • We have seen only left-handed neutrinos and right-handed anti-neutrinos (CPT) • Neutrinos are strictly massless in the Standard Model Finite mass of neutrinos implies that the Standard Model is incomplete! • Not just incomplete but probably a lot more profound Erice 2005

  20. Mass Spectrum What do we do now? Erice 2005

  21. (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 Erice 2005

  22. Extra Dimensions • All charged particles are on a 3-brane • 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 • Or anomaly mediated SUSY breaking (Arkani-Hamed, Kaplan, HM, Nomura) Erice 2005

  23. (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 Erice 2005

  24. 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!) Erice 2005

  25. 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 Neutrino mass may be probing unification: Einstein’s dream Erice 2005

  26. Seven Questions

  27. Three-generation Framework • Standard parameterization of MNS matrix for 3 generations atmospheric ??? solar Erice 2005

  28. Three-generation • Solar, reactor, atmospheric and K2K data easily accommodated within three generations • sin22q23near maximal Dm2atm ~ 2.510–3eV2 • sin22q12large Dm2solar ~810–5eV2 • sin22q13=|Ue3|2< 0.05 from CHOOZ, Palo Verde • Because of small sin22q13, solar (reactor) & atmospheric n oscillations almost decouple Maltoni et al, hep-ph/0405172 Erice 2005

  29. Six Seven Questions • Dirac or Majorana? • Absolute mass scale? • How small is q13? • CP Violation? • Mass hierarchy? • Verify Oscillation? • LSND? Sterile neutrino(s)? CPT violation? Erice 2005

  30. KamLAND oscillation • Now strong evidence that neutrinos do disappear and reappear (and again) Oscillation! Erice 2005

  31. Neutrinoless Double-beta Decay • The only known practical approach to discriminate Majorana vs Dirac neutrinos 0nbb: nn  ppe–e– with no neutrinos • Matrix element  <mne>=SimniUei2 • Current limit |<mne>| ≤ about 1eV Erice 2005

  32. Three Types of Mass Spectrum • Degenerate • All three around >0.1eV with small splittings • Laboratory limit: m<2.3eV • May be confirmed by KATRIN, cosmology • |<mne>|=|SimniUei2|>m cos22q12>0.07m • Inverted • m3~0, m1~m2~(Dm223)1/2≈0.05eV • May be confirmed by long-baseline experiment with matter effect • |<mne>|=|SimniUei2|>(Dm223)1/2 cos22q12>0.013eV (HM, Peña-Garay) • Normal • m1~m2~0, m3~(Dm223)1/2≈0.05eV • |<mne>|=|SimniUei2| may be zero even if Majorana Erice 2005

  33. Cosmological Limit • CMB+LSS+Lyman a(Seljak et al, astro-ph/0407372): Simi<0.42 eV, m1<0.13 eV (95% CL) • Puts upper limit on the effective neutrino mass in the neutrinoless double beta decay (Pierce, HM) • |<mne>|=|SimniUei2|<Simni |Uei2|<0.13eV • Heidelberg-Moscow: |<mne>|=0.11–0.56 eV • Reanalysis with Vogel’s MEs: |<mne>|=0.4–1.3 eV Erice 2005

  34. Cosmology vs Laboratory • Global fit to the “World Data” • indeed, tension between the Heidelberg-Moscow claim and cosmology • Still subject to the uncertainties in nuclear matrix element (Bahcall, HM, Peña-Garay) • Better data and theory needed! Lisi et al, hep-ph/0408045 Erice 2005

  35. Why do we exist?Matter Anti-matter Asymmetry

  36. Erice 2005

  37. Matter and Anti-MatterEarly Universe 10,000,000,001 10,000,000,000 Matter Anti-matter Erice 2005

  38. Matter and Anti-MatterCurrent Universe us 1 Matter Anti-matter The Great Annihilation Erice 2005

  39. Baryogenesis • Gaussian scale-invariant fluctuation  inflation • Initial condition wiped out • What created this tiny excess matter? • Necessary conditions for baryogenesis (Sakharov): • Baryon number non-conservation • CP violation (subtle difference between matter and anti-matter) • Non-equilibrium  G(DB>0) > G(DB<0) • It looks like neutrinos have no role in this… Erice 2005

  40. Actually, SM converts L (n) to B (quarks). In Early Universe (T > 200GeV), W is massless and fluctuate in W plasma Energy levels for left-handed quarks/leptons fluctuate correspon-dingly DL=DQ=DQ=DQ=DB=1  D(B–L)=0 Electroweak Anomaly Erice 2005

  41. Leptogenesis • You generate Lepton Asymmetry first. (Fukugita, Yanagida) • Generate L from the direct CP violation in right-handed neutrino decay • L gets converted to B via EW anomaly  More matter than anti-matter  We have survived “The Great Annihilation” • Despite detailed information on neutrino masses, it still works! (e.g., Bari, Buchmüller, Plümacher)

  42. Maybe an even bigger role: inflation Need a spinless field that slowly rolls down the potential oscillates around it minimum decays to produce a thermal bath The superpartner of right-handed neutrino fits the bill When it decays, it produces the lepton asymmetry at the same time (HM, Suzuki, Yanagida, Yokoyama) Decay products: supersymmetry and hence dark matter Neutrino is mother of the Universe? ~ R Origin of Universe amplitude size of the universe Erice 2005

  43. Origin of the Universe • Right-handed scalar neutrino: V=m2f2 • ns=0.96 • r=0.16 • Detection possible in the near future Erice 2005

  44. Can we prove it experimentally? • 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 Erice 2005

  45. Models of Flavor

  46. Question of Flavor • What distinguishes different generations? • Same gauge quantum numbers, yet different • Hierarchy with small mixings:  Need some ordered structure • Probably a hidden flavor quantum number  Need flavor symmetry • Flavor symmetry must allow top Yukawa • Other Yukawas forbidden • Small symmetry breaking generates small Yukawas • Repeat Gell-Mann Okubo! Erice 2005

  47. Broken Flavor Symmetry • Flavor quantum numbers (SU(5)-like): • 10(Q, uR, eR) (+2, +1, 0) • 5*(L, dR) (+1, +1, +1) • Flavor symmetry broken by a VEV ~0.02 • mu:mc:mt~ md2:ms2:mb2~ me2:mm2:mt2 ~4: 2:1 Erice 2005

  48. Not bad! • mb~ 3mt, ms ~ 3mm, md ~ 3me • mu:mc:mt~ md2:ms2:mb2~ me2:mm2:mt2 Erice 2005

  49. New Insight from Neutrinos • Neutrinos are already providing significant new information about flavor symmetries • If LMA, all mixing except Ue3 large • Two mass splittings not very different • Atmospheric mixing maximal • Any new symmetry or structure behind it? Erice 2005

  50. Is There a Structurein Neutrino Masses & Mixings? • Monte Carlo random complex 33 matrices with seesaw mechanism (Hall, HM, Weiner; Haba, HM) Erice 2005

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