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

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

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5 LSND

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7 3.3  Signal Excess positron events over calculated BG

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

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

10 SN1987A neutrino burst doesn’t like LSND HM, Yanagida

11 Sterile Neutrino LSND, atmospheric and solar neutrino oscillation signals  m 2 LSND ~ eV 2  m 2 atm ~ 3  10 –3 eV 2  m 2 solar < 10 –3 eV 2   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?

12 Sterile Neutrino getting tight 3+1 spectrum: sin 2 2  LSND =4|U 4e | 2 |U 4  | 2 –|U 4  | 2 can’t be big because of CDHS, SK U/D –|U 4e | 2 can’t be big because of Bugey –Marginally allowed (90% excl. vs 99% allw’d) 2+2 spectrum: past fits preferred –Atmospheric mostly    –Solar mostly e  s (or vice versa) –Now solar sterile getting tight (Barger et al, Giunti et al, Gonzalez-Garcia et al, Strumia)

13 Not Quite Excluded Yet… Global fit to four- neutrino oscillation –Solar, Atmospheric, LSND (Gonzalez-Garcia, Maltoni, Peña- One can still find a reasonable fit with 2+2  Disfavored at 90-99% CL e  s    e     s

14 CPT Violation? “A desperate remedy…” 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)

15 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)

16 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!

17 Maybe even more surprises in neutrinos!

Implications of Neutrino Mass

19 Mass Spectrum What do we do now?

20 Two ways to go (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?

21 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) m ~ 1/R if one extra dim  R~10  m An infinite tower of sterile neutrinos Need also inter-generational mixing now

22 Two ways to go (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!

23 Seesaw Mechanism Why is neutrino mass so small? Need right-handed neutrinos to generate neutrino mass To obtain m 3 ~(  m 2 atm ) 1/2, m D ~m t, M 3 ~10 15 GeV (GUT!), but R SM neutral

24 Grand Unification electromagnetic, weak, and strong forces have very different strengths But their strengths become the same at GeV if supersymmetry To obtain m 3 ~(  m 2 atm ) 1/2, m D ~m t  M 3 ~10 15 GeV! Neutrino mass may be probing unification: Einstein’s dream M3M3 Dimopoulos, Raby, Wilczek

Matter Anti-matter Asymmetry Why do we exist?

26 Big-Bang Nucleosynthesis Cosmic Microwave Background (Thuan, Izatov) (Burles, Nollett, Turner)

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28 Baryon Asymmetry Early Universe They basically have all annihilated away except a tiny difference between them 10,000,000,00110,000,000,000

29 Baryon Asymmetry Current Universe They basically have all annihilated away except a tiny difference between them 1 us

30 Sakharov’s Conditions for Baryogenesis Necessary requirements for baryogenesis: –Baryon number violation –CP violation –Non-equilibrium  (  B>0) >  (  B<0) Possible new consequences in –Proton decay –CP violation

31 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:  ’! But keeps B–L  0  “anomaly washout” Also monopole problem

32 Anomaly washout 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  L=  Q=  Q=  Q=  B=1  B=L=0

33 Two Main Directions B  L  0 gets washed out at T>T EW ~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

Leptogenesis

35 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”

36 Does Leptogenesis Work? Much more details worked out (Buchmüller, Plümacher; Pilaftsis) ~10 10 GeV R OK Some tension with supersymmetry because of unwanted gravitino overproduction Ways around: coherent oscillation of right- handed sneutrino (HM, Yanagida+Hamaguchi)

37 Does Leptogenesis Work? Some tension with supersymmetry: –unwanted gravitino overproduction –gravitino decay dissociates light nuclei –destroys the success of Big-Bang Nucleosynthesis –Need T RH <10 9 GeV (Kawasaki, Kohri, Moroi)

38 Leptogenesis Works! 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

39 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 –0  found –CP violation found in neutrino oscillation –EW baryogenesis ruled out Archeological evidences

40 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