Neutrino Physics III Hitoshi Murayama University of Pisa

Neutrino Physics III Hitoshi Murayama University of Pisa February 26, 2003

Outline • • • Three Generations LSND Implications of Neutrino Mass Why do we exist? Models of flavor Conclusions 2

Three Generations

MNS matrix • Standard parameterization of Maki. Nakagawa-Sakata matrix for 3 generations atmospheric ? ? ? solar 4

Three-generation • Solar & atmospheric n oscillations easily accommodated within three generations • sin 22 q 23 near maximal, Dm 2 atm ~ 3 10– 3 e. V 2 • sin 22 q 12 large, Dm 2 solar ~ 5 10– 5 e. V 2 • sin 22 q 13 < 0. 05 from CHOOZ, Palo Verde • Because of small sin 22 q 13, solar & atmospheric n oscillations almost decouple • Need to know sin 22 q 13, and mass hierarchy 5

Raised More Questions • Why do neutrinos have mass at all? • Why so small? • We have seen mass differences. What are the masses? Wn~mn/15 e. V • Do we need a fourth neutrino? • Are neutrinos and antineutrinos the same? • How do we extend the Standard Model to incorporate massive neutrinos? 6

3 -flavor mixing • If m 1 and m 2 not very different, it reduces to the 2 -flavor problem 7

When is 3 -flavor important? When all masses significantly different Anti-neutrinos: U U*, the last term flips sign Possible CP violation 8

CP Violation • Possible only if: – Dm 122, s 12 large enough (LMA) – q 13 large enough 9

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LSND 11

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3. 3 s Signal • Excess positron events over calculated BG 13

Mini-Boo. NE • LSND unconfirmed • Neutrino beam from Fermilab booster • Settles the issue of LSND evidence • Started data taking the summer 2002 14

LSND Affects SN 1987 A neutrino burst • Kamiokande’s 11 events: – 1 st 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 n_e n_m if light side (ne lighter) ne nm if dark side (ne heavier) • Either mass spectrum disfavored HM, Yanagida 15

LSND Affects SN 1987 A neutrino burst HM, Yanagida 16

Sterile Neutrino • LSND, atmospheric and solar neutrino oscillation signals • 3+1 or 2+2 spectrum? Dm 2 LSND ~ e. V 2 Dm 2 atm ~ 3 10– 3 e. V 2 Dm 2 solar < 10– 3 e. V 2 Can’t be accommodated with 3 neutrinos Need a sterile neutrino New type of neutrino with no weak interaction 17

Sterile Neutrino getting tight • 3+1 spectrum: sin 22 q. LSND=4|U 4 e|2|U 4 m|2 – |U 4 m|2 can’t be big because of CDHS, SK U/D – |U 4 e|2 can’t be big because of Bugey – Marginally allowed • 2+2 spectrum: past fits preferred – Atmospheric mostly nm nt – Solar mostly ne ns (or vice versa) – Now pretty much ruled out (Barger et al, Giunti et al, Gonzalez-Garcia et al, Strumia, Maltoni et al) 18

WMAP Maltoni, Schwetz, Tortola, Valle hep-ph/0209368 19

CPT Violation? “A desperate remedy…” • LSND evidence: anti-neutrinos • Solar evidence: neutrinos • If neutrinos and anti-neutrinos have different mass spectra, atmospheric, solar, LSND accommodated without a sterile neutrino (HM, Yanagida) (Barenboim, Lykken, et al) Best fit to data before Kam. LAND (Strumia) 20

Kam. LAND impact • However, now there is an evidence for “solar” oscillation in anti-neutrinos from Kam. LAND • Barenboim, Borissov, Lykken: evidence for atmospheric neutrino oscillation is dominantly for neutrinos. Antineutrinos suppressed by a factor of 3. • Not a great fit (Strumia) • New CPT violation: 21

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-local Hamiltonian? (HM, Yanagida) – Brane world? (Barenboim, Borissov, Lykken, Smirnov) – Dipole Field Theory? (Bergman, Dasgupta, Ganor, Karczmarek, Rajesh) 22

Implications on Experiments • Mini-Boo. NE experiment will not see oscillation in neutrino mode, but will in anti-neutrino mode • Because Kam. LAND is consistent with LMA, atmospheric neutrino oscillation relies on Dm 2 LSND ~ e. V 2 (not a great fit) • Katrin may see _ endpoint spectrum distortion in t 3 He+e–+ne We’ll see! 23

Maybe even more surprises in neutrinos! 24

Mass Spectrum What do we do now? 25

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 weakly coupled – Why? 26

Extra Dimension • 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) • Barbieri-Strumia: SN 1987 A constraint “Warped” extra dimension (Grossman, Neubert) • Or SUSY breaking (Arkani-Hamed, Hall, HM, Smith, Weiner; Arkani-Hamed, Kaplan, HM, Nomura) 27

Two ways to go (2) Majorana Neutrinos: – There are no new light particles – What if I pass a neutrino and look back? – Must be right-handed anti-neutrinos – No fundamental distinction between neutrinos and antineutrinos! 28

Seesaw Mechanism • Why is neutrino mass so small? • Need right-handed neutrinos to generate neutrino mass , but n. R SM neutral To obtain m 3~(Dm 2 atm)1/2, m. D~mt, M 3~1015 Ge. V (GUT!) 29

Grand Unification • electromagnetic, weak, and strong forces have very different strengths • But their strengths become the same at 1016 Ge. V if supersymmetry • To obtain m 3~(Dm 2 atm)1/2, m. D~mt M 3~1015 Ge. V! M 3 Neutrino mass may be probing unification: Einstein’s dream 30

Why do we exist? Matter Anti-matter Asymmetry

Big-Bang Nucleosynthesis Cosmic Microwave Background WMAP (Thuan, Izatov) (Burles, Nollett, Turner) 32

Matter and Anti-Matter Early Universe 10, 000, 001 10, 000, 000 Matter Anti-matter 33

Matter and Anti-Matter Current Universe us 1 Matter Anti-matter The Great Annihilation 34

Sakharov’s Conditions for 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 35

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 36

Electroweak Anomaly • Actually, SM converts L to B. – In Early Universe (T > 200 Ge. V), W/Z are massless and fluctuate in W/Z plasma – Energy levels for lefthanded quarks/leptons fluctuate correspondingly DL=DQ=DQ=DQ=DB=1 D(B–L)=0 37

Two Main Directions • B L 0 gets washed out at T>TEW~174 Ge. V • 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 38

Leptogenesis • You generate Lepton Asymmetry first. • 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” 39

Does Leptogenesis Work? • Much more details worked out (Buchmüller, Plümacher; Pilaftsis) • ~1010 Ge. V n. R OK • Some tension with supersymmetry because of unwanted gravitino overproduction • Ways around: coherent oscillation of righthanded sneutrino (HM, Yanagida+Hamaguchi) 40

Does Leptogenesis Work? • Some tension with supersymmetry: – unwanted gravitino overproduction – gravitino decay dissociates light nuclei – destroys the success of Big-Bang Nucleosynthesis – Need TRH<109 Ge. V (Kawasaki, Kohri, Moroi) 41

Leptogenesis Works! • Coherent oscillation of righthanded 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 perturbation at WMAP? (Moroi, HM) 42

Can we prove it experimentally? • We studied this question at Snowmass 2001 (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 nbb found – CP violation found in neutrino oscillation – EW baryogenesis ruled out Archeological evidences 43

Models of Flavor

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 45

Fermion Mass Relation in SU(5) • down- and lepton-Yukawa couplings come from the same SU(5) operator 10 5* H • Fermion mass relation mb= mt, ms = mm, md = me @MGUT Reality: mb≈ mt, 3 ms ≈ mm, md ≈ 3 me @MGUT • Not bad! (small correction compared to inter -generational splitting ~20– 200) 46

Broken Flavor Symmetry • Flavor symmetry broken by a VEV ~0. 02 • SU(5)-like: – 10(Q, u. R, e. R) (+2, +1, 0) – 5*(L, d. R) (+1, +1) – mu: mc: mt ~ md 2: ms 2: mb 2 ~ me 2: mm 2: mt 2 ~ 4: 2 : 1 47

Not bad! • mb~ mt, ms ~ mm, md ~ me @MGUT • mu: mc: mt ~ md 2: ms 2: mb 2 ~ me 2: mm 2: mt 2 48

New Data from Neutrinos • Neutrinos are already providing significant new information about flavor symmetries • If LMA, all mixing except Ue 3 large – Two mass splittings not very different – Atmospheric mixing maximal – Any new symmetry or structure behind it? 49

Is There A Structure In Neutrino Masses & Mixings? • Monte Carlo random complex 3 3 matrices with seesaw mechanism (Hall, HM, Weiner; Haba, HM) 50

Anarchy • No particular structure in neutrino mass matrix – All three angles large – CP violation O(1) – Ratio of two mass splittings just right for LMA • Three out of four distributions OK – Reasonable Underlying symmetries don’t distinguish 3 neutrinos. 51

q 13 in Anarchy • q 13 cannot be too small if anarchy • How often can “large” angle fluctuate down to the CHOOZ limit? • Kolmogorov–Smirnov test: 12% • sin 2 2 q 13>0. 004 (3 s) • If so, CP violation observable at long baseline experiment 52

Anarchy is Peaceful • Anarchy (Miriam-Webster): “A utopian society of individuals who enjoy complete freedom without government” • Peaceful ideology that neutrinos work together based on their good will • Predicts large mixings, LMA, large CP violation • sin 22 q 13 just below the bound • Ideal for VLBL experiments • Wants globalization! 53

Program: More flavor parameters • Squarks, sleptons also come with mass matrices • Off-diagonal elements violate flavor: suppressed by flavor symmetries • Look for flavor violation due to SUSY loops • Then look for patterns to identify symmetries Repeat Gell-Mann–Okubo! • Need to know SUSY masses 54

To Figure It Out… • Models differ in flavor quantum number assignments • Need data on sin 22 q 13, solar neutrinos, CP violation, B-physics, LFV, EWSB, proton decay • Archaeology • We will learn insight on origin of flavor by studying as many fossils as possible – cf. CMBR in cosmology 55

More Fossils: Lepton Flavor Violation • Neutrino oscillation lepton family number is not conserved! – – – Any tests using charged leptons? Top quark unified with leptons Slepton masses split in up- or neutrino-basis Causes lepton-flavor violation (Barbieri, Hall) predict B(t mg), B(m eg), m e at interesting (or toolarge) levels 56

Barbieri, Hall, Strumia 57

More Fossils: Quark Flavor Violation • Now also large mixing between nt and nm – (nt, b. R) and (nm , s. R) unified in SU(5) – Doesn’t show up in CKM matrix – But can show up among squarks – CP violation in Bs mixing (Bs J/y f) – Addt’l CP violation in penguin b s (Bd f Ks) (Chang, Masiero, HM) 58

Conclusions

Conclusions • Historic era in neutrino physics • Oscillation in atmospheric neutrino: an unexpected discovery, strong evidence for neutrino mass • Decades-long problem in solar neutrinos now being resolved • A lot more to learn in the near future • Interesting connections to cosmology, astrophysics • We’d like to know how to build the new Standard Model! 60