Origin of Neutrino Mass

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

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!

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

?
6
Rare Effects from High-Energies

• Effects of physics beyond the SM as effective
  operators
• Can be classified systematically (Weinberg)

7
Unique Role of Neutrino Mass

• Lowest order effect of physics at short distances
• Tiny effect (mn/En)2(eV/GeV)21018!
• 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

8
Ubiquitous Neutrinos
9
Sun as a neutrino source
SuperK image of the Sun
10
We dont get enough
We need survival probabilities of 8B 1/3 7Be
lt1/3 pp 2/3 Can we get three numbers correctly
with two parameters?
11
Year of Neutrino 2002
March 2002
April 2002 with SNO
Dec 2002 with KamLAND
12
Solar Neutrino Problem Finally Solved After 35
Years!
13
Historic Era in Neutrino Physics

• We learned
• Atmospheric nms are lost. P4.2 1026 (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

14
CP Violation

• Possible only if
• Dm122, s12 large enough (LMA)
• q13 large enough
• Can we see CP violation?

15
Typical Theorists View ca. 1990

• Solar neutrino solution must be small angle MSW
  solution because its cute
• Natural scale for Dm223 10100 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!
16
Implications of Neutrino Mass
17
Neutrinos are Left-handed
18
Neutrinos must be Massless

• All neutrinos left-handed ? massless
• If they have mass, cant go at speed of light.

• Now neutrino right-handed??
• ? contradiction ? cant be massive

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

20
Mass Spectrum
What do we do now?
21
Two ways to go

• (1) Dirac Neutrinos
• There are new particles, right-handed neutrinos,
  after all
• Why havent we seen them?
• Right-handed neutrino must be very very weakly
  coupled
• Why?

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 ? R10mm
• An infinite tower of sterile neutrinos
• Or anomaly mediated SUSY breaking
• (Arkani-Hamed, Kaplan, HM, Nomura)

23
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!

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, mDmt, M31015GeV (GUT!)
25
Grand Unification
M3

• 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, mDmt
• ? M31015GeV!

Neutrino mass may be probing unification Einstein
s dream
26
Seven Questions
27
Three-generation Framework

• Standard parameterization of MNS matrix for 3
  generations

atmospheric
???
solar
28
Three-generation

• Solar, reactor, atmospheric and K2K data easily
  accommodated within three generations
• sin22q23 near maximal Dm2atm
  2.5?103eV2
• sin22q12 large Dm2solar 8?105eV2
• sin22q13Ue32lt 0.05 from CHOOZ, Palo Verde
• Because of small sin22q13, solar (reactor)
  atmospheric n oscillations almost decouple

Maltoni et al, hep-ph/0405172
29
Seven Questions

• Dirac or Majorana?
• Absolute mass scale?
• How small is q13?
• CP Violation?
• Mass hierarchy?
• Verify Oscillation?
• LSND? Sterile neutrino(s)? CPT violation?

30
KamLAND oscillation

• Now strong evidence that neutrinos do disappear
  and reappear (and again)

Oscillation!
31
Neutrinoless Double-beta Decay

• The only known practical approach to discriminate
  Majorana vs Dirac neutrinos
• 0nbb nn ? ppee with no neutrinos
• Matrix element ? ltmnegtSimniUei2
• Current limit
• ltmnegt about 1eV

32
Three Types of Mass Spectrum

• Degenerate
• All three around gt0.1eV with small splittings
• Laboratory limit mlt2.3eV
• May be confirmed by KATRIN, cosmology
• ltmnegtSimniUei2gtm cos22q12gt0.07m
• Inverted
• m30, m1m2(Dm223)1/20.05eV
• May be confirmed by long-baseline experiment with
  matter effect
• ltmnegtSimniUei2gt(Dm223)1/2 cos22q12gt0.013eV
  (HM, Peña-Garay)
• Normal
• m1m20, m3(Dm223)1/20.05eV
• ltmnegtSimniUei2 may be zero even if Majorana

33
Cosmological Limit

• CMBLSSLyman a (Seljak et al, astro-ph/0407372)
  
• Si m?ilt0.42 eV, m?1lt0.13 eV (95 CL)
• Puts upper limit on the effective neutrino mass
  in the neutrinoless double beta decay (Pierce,
  HM)
• ltmnegtSimniUei2ltSimni Uei2lt0.13eV
• Heidelberg-Moscow ltmnegt0.110.56 eV
• Reanalysis with Vogels MEs ltmnegt0.41.3 eV

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
35
Why do we exist?Matter Anti-matter Asymmetry
36
(No Transcript)
37
Matter and Anti-MatterEarly Universe
10,000,000,001
10,000,000,000
Matter
Anti-matter
38
Matter and Anti-MatterCurrent Universe
us
1
Matter
Anti-matter
The Great Annihilation
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(DBgt0) gt G(DBlt0)
• It looks like neutrinos have no role in this

40
Electroweak Anomaly

• Actually, SM converts L (n) to B (quarks).
• In Early Universe (T gt 200GeV), W is massless and
  fluctuate in W plasma
• Energy levels for left-handed quarks/leptons
  fluctuate correspon-dingly

• DLDQDQDQDB1 ? D(BL)0

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
Origin of Universe

?R

• 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?

amplitude
size of the universe
43
Origin of the Universe

• Right-handed scalar neutrino Vm2f2
• ns0.96
• r0.16
• Detection possible in the near future

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

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!

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
• mumcmt md2ms2mb2 me2mm2mt2 ?4 ?2 1

48
Not bad!

• mb 3mt, ms 3mm, md 3me
• mumcmt md2ms2mb2 me2mm2mt2

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?

50
Is There a Structurein Neutrino Masses Mixings?

• Monte Carlo random complex 3?3 matrices with
  seesaw mechanism
• (Hall, HM, Weiner Haba, HM)

51
Anarchy

• Reasonable distributions from randomness
• ? Underlying symmetries dont distinguish 3
  neutrinos.
• Flavor quantum numbers
• 10(Q, uR, eR) (2, 1, 0)
• 5(L, dR) (1, 1, 1)
• Inconceivable just a few years ago

52
q13 in Anarchy

• q13 cannot be too small if anarchy
• How often can large angle fluctuate down to the
  CHOOZ limit?
• KolmogorovSmirnov test 12
• sin2 2q13gt0.004 (3s)
• CP violation likely observable at long baseline
  experiment

(de Gouvêa, HM)
53
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
• sin22q13 just below the bound
• Ideal for superbeam, n-factory
• ? Pro-globalization!

54
Different Flavor Symmetries

• Altarelli-Feruglio-Masina hep-ph/0210342

Hall, HM, Weiner
Sato, Yanagida Vissani
Barbieri et al
55
Critical Measurements

• sin2 2q231.00?0.01?
• Determines a need for a new symmetry to enforce
  the maximal mixing
• sin2 2q13lt0.01?
• Determines if the flavor quantum number of
  electron is different from mu, tau
• Normal or inverted hierarchy?
• Most symmetries predict the normal hierarchy
• CP Violation?
• Plausibility test of leptogenesis

56
Large q23 and quarks

• Large mixing between nt and nm
• Make it SU(5) GUT
• Then a large mixing between sR and bR
• Mixing among right-handed fields drop out from
  CKM matrix
• But mixing among superpartners physical
• O(1) effects on b?s transition possible
• (Chang, Masiero, HM)
• Expect CP violation in neutrino sector especially
  if leptogenesis
• Bs?J/y f?? Bd?f Ks

57
More FossilsLepton 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
  too-large) levels

58
Dynamics behind flavor symmetry?

• Once flavor symmetry structure identified (e.g.,
  Gell-ManOkubo), what is dynamics? (e.g., QCD)

• Supersymmetry
• Anomalous U(1) gauge symmetry with Green-Schwarz
  mechanism
• Large Extra Dimensions
• Fat brane with physically separated left- and
  right-handed particles
• Technicolor
• New broken gauge symmetries at 100TeV scale

59
Conclusions

• Revolutions in neutrino physics
• The solar neutrino problem solved!
• Small but finite neutrino mass
• Probes physics beyond the standard model
• New insights into the origin of flavor
• Interesting interplay between neutrinos and
  cosmos
• Neutrino mass may be responsible for our
  existence
• Neutrinos may even be the origin of the universe
• A lot more to learn in the next few years

60
(No Transcript)
61
(No Transcript)