Theoretical Neutrino Physics

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Theoretical Neutrino Physics

• Hitoshi Murayama (Berkeley)
• EPS 2003 _at_ Aachen
• July 22, 2003

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Milind Diwan

• Neutrino physics is so simple. There are no
  hadronic corrections. We dont need theorists.

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Why You Need Theoristsin Neutrino Physics

• Hitoshi Murayama (Berkeley)
• EPS 2003 _at_ Aachen
• July 22, 2003

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Outline

• A Little Historical Perspective
• Interpretation of Data Seven Questions
• Solar Neutrino
• Interpretation without LSND
• Interpretation with LSND
• Nature of neutrino mass
• Models of Flavor
• Conclusions

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A Little Historical Perspective
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Rare Effects from High-Energies

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

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Unique Role of Neutrino Mass

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

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Grand Unification

• electromagnetic, weak, and strong forces have
  very different strengths
• But their strengths become the same at 1016 GeV
  if supersymmetry
• A natural candidate energy scale L1016GeV
• ? mn0.003eV
• mn(Dm2atm)1/20.03eV
• mn(Dm2LMA)1/20.007eV

Neutrino mass may be probing unification!
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Interpretation of DataSeven Questions
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What we learned since Budapest

• Atmospheric nms are lost. P4.2 1026 (SK,
  Hayato)
• converted most likely to nt (gt99CL)
• Solar ne is converted to either nm or nt (gt5s)
  (SNO, Poon)
• Reactor anti-ne are lost (99.95CL) (KamLAND,
  Lesko)
• Only the LMA solution left for solar neutrinos
• Tiny neutrino mass the first evidence for
  incompleteness of Minimal Standard Model

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Solar Neutrino Problem Finally Solved After 35
Years!
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SNO Result

• Only ne produced in the Sun
• Wrong Neutrinos nm,t are coming from the Sun!
• Somehow some of ne were converted to nm,t on
  their way from the Suns core to the detector
• ? neutrino flavor conversion!

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KamLAND result

• First terrestrial expt relevant to solar neutrino
  problem

Dec 2002 Expected events 86.85.6 Background
events 0.950.99 Observed events 54
No oscillation hypothesis Excluded at 99.95
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No other solution than oscillation

• Neutrino decay
• Wrong energy dependence
• Spin-resonant flip
• Relies on a large solar magnetic field
• New flavor-changing neutral current
• Relies on a high solar matter density
• Violation of the equivalence principle
• Relies on the strong solar gravitational potential

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Progress in 2002 on the Solar Neutrino Problem
March 2002
April 2002 with SNO
Dec 2002 with KamLAND
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Solar Neutrino Spectrum
pp
7Be
8B
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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?
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Matter Effect

• CC interaction in the presence of
  non-relativistic electron

• Neutrino Hamiltonian

Electron neutrino higher energy in the Sun
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Adiabatic

• Use instantaneous eigenstates n and n

• For the LMA region, the dynamics is adiabatic
  there is no hopping between states

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Solar Neutrino Astrophysics

• Davis and Bahcall started solar neutrino work
  because they wanted to probe physics of the sun
• Finally one can fit all solar neutrino data
  together with KamLAND to measure all major
  components pp, 7Be, 8B (Bahcall, Peña-Garay)
• Solar luminosity confirmed

• Possible concern density perturbation (Reggiani)

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Loose Ends

• Energy dependence in the solar neutrino survival
  probability not fully demonstrated
• pp, 7Be solar neutrino experiments
• Nobody has seen oscillation, i.e., the survival
  probability dips and comes back up
• Atmospheric MINOS
• Solar/reactor continued KamLAND
• Evidence for nt appearance in atmos n still not
  strong enough (99CL)
• OPERA, ICARUS

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Low-Energy Solar Neutrinos

• Solar neutrino data suggest energy-dependent
  survival probability
• ? tests MSW effect
• ? q12
• ? Helps interpretation of CP violation, double
  beta decay data

1
7
20
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Verify Oscillation

• Even atmospheric neutrino data do not show
  oscillation yet
• ? MINOS, J-PARC
• ? Dm223, q23, mass hierarchy and q13
• KamLAND data is consistent with overall
  suppression
• ? continued running
• ? Dm212

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Interpretation Without LSND
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Three-generation Framework

• Standard parameterization of MNS matrix for 3
  generations

atmospheric
solar
???
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Three-generation

• Solar, reactor, atmospheric and K2K data easily
  accommodated within three generations
• sin22q23 near maximal Dm2atm 3?103eV2
• sin22q12 large Dm2solar 7?105eV2
• sin22q13Ue32lt 0.05 from CHOOZ, Palo Verde
• Because of small sin22q13, solar (reactor)
  atmospheric n oscillations almost decouple

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Seven Questions

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

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Seven Questions

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

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Now that LMA is confirmed...

• Dream case for neutrino oscillation physics!
• Dm2solar within reach of long-baseline expts
• Even CP violation may be probable
• neutrino superbeam
• muon-storage ring neutrino factory
• Possible only if
• Dm122, s12 large enough (LMA)
• q13 large enough

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q13 decides the future

• The value of q13 crucial for the future of
  neutrino oscillation physics
• Determines the required facility/parameters/baseli
  ne/energy
• Two paths to determine q13
• Long-baseline accelerator neutrino oscillation
• Reactor neutrino experiment with two detectors

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Shootout (Lindner)
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Seven Questions

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

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Intepretation With LSND
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3.3s Signal

• Excess positron events over calculated BG

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Sterile Neutrino

• LSND, atmospheric and solar neutrino oscillation
  signals
• Dm2LSND eV2
• Dm2atm 3?103eV2
• Dm2solar lt 103eV2
• ?? Cant be accommodated with 3 neutrinos
• ?? Need a sterile neutrino
• New type of neutrino with no weak interaction

• 31 or 22 spectrum?

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Sterile Neutrino disfavored

• 22 spectrum past fits preferred
• Atmospheric mostly nm?nt
• Solar mostly ne?na (or vice versa)
• Now solar sterile getting tight due to SNO
• Disfavored 1.6 106 (Maltoni et al)
• 31 spectrum sin22qLSND4U4e2U4m2
• U4m2 cant be big because of CDHS, SK U/D
• U4e2 cant be big because of Bugey
• Disfavored 5.6 103 (Maltoni et al)

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More Sterile Neutrinos?

• Who said there is only one sterile neutrino?
• There could well be one for each generation
• Do more sterile neutrinos help?

• Maybe 32 better (Sorel, Conrad, Shaevitz)

PLSNDlt0.10
PLSNDlt 0.20
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WMAP2dFLyman a
Maltoni, Schwetz, Tortola, Valle hep-ph/0209368
?m?lt0.7eV (95)
Spergel et al
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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)
• Best fit to data before KamLAND
• (Strumia)

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KamLAND impact

• However, now there is an evidence for solar
  oscillation in anti-neutrinos from KamLAND
• Barenboim, Borissov, Lykken evidence for
  atmospheric neutrino oscillation is dominantly
  for neutrinos. Anti-neutrinos suppressed by a
  factor of 3.

• New CPT violation

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KamLAND impact

• However, now there is an evidence for solar
  oscillation in anti-neutrinos from KamLAND
• Barenboim, Borissov, Lykken evidence for
  atmospheric neutrino oscillation is dominantly
  for neutrinos. Anti-neutrinos suppressed by a
  factor of 3.
• However fit not good (Gonzalez-Garcia, Maltoni,
  Schwetz)
• MINOS atmospheric data will settle this

• New CPT violation

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LSND not as oscillation

• Maybe LSND detected anomalous decay of muon
  (Babu, Pakvasa)
• Lepton-number violation
• KARMEN disfavors it
• BRlt0.009 (90) while LSND wants BR0.0190.040
• No signal at Mini-BooNE
• Predicts Michel parameter r0.7485?0.75
• Current accuracy r0.75180.0026
• TWIST experiment at TRIUMF measures Michel
  parameter down to a few times 104

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Seven Questions

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

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Extended Standard Model

• Massive Neutrinos ? Minimal SM incomplete
• How exactly do we extend it?
• Abandon either
• Minimality introduce new unobserved light
  degrees of freedom (right-handed neutrinos)
• Lepton number abandon distinction between
  neutrinos and anti-neutrinos and hence matter and
  anti-matter
• Dirac or Majorana neutrino
• Without knowing which, we dont know how to
  extend the Standard Model

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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!) Neutrinos are Majorana
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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
• m3Ue32ltltm3 and we can typically ignore m3
• ltmnegtm1cos2q12eif m2sin2q12
• possible cancellation due to unknown Majorana
  phase
• Fortunately, they cannot cancel exactly because
  the maximal angle q12 excluded by SNO
  cos2q12sin2q12cos22q12gt0.07 (1s)

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Three Types of Mass Spectrum

• Degenerate
• All three around gt0.1eV with small splittings
• Possible even after WMAP2dF mlt0.23eV
• 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 cos22q12gt0.0035eV
• Normal
• m1m20, m3(Dm223)1/20.05eV
• ltmnegtSimniUei2 may be zero even if Majorana

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WMAP again

• WMAP constraint
• m?lt0.23eV each (95CL)
• Puts upper limit on the effective neutrino mass
  in the neutrinoless double beta decay (Pierce,
  HM)
• ltmnegtSimniUei2ltSimni Uei2lt0.23eV
• Heidelberg-Moscow ltmnegt0.110.56 eV
• Reanalysis by Vogel ltmnegt0.41.3 eV

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Models of Flavor
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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 of the order of Vcb
• Atmospheric neutrino anomaly must go away because
  it needs a large angle

Wrong!
Wrong!
Wrong!
Wrong!
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Surprises

• Prejudice from quarks, charged leptons
• Mixing angles are small
• Masses are hierarchical
• In LMA, all mixing except Ue3 large
• Two mass splittings not very different
• Atmospheric mixing maximal
• Any new symmetry or structure behind it?

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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
• Try to find underlying symmetries from data
  (bottom-up)
• Repeat Heisenberg, Gell-MannOkubo

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Different Flavor Symmetries

• Altarelli-Feruglio-Masina hep-ph/0210342

Hall, HM, Weiner
Sato, Yanagida Vissani
Barbieri et al
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Lack of symmetry explains data
3-D KolmogorovSmirnov test (de Gouvêa, HM)

• Suppose there is no symmetry behind the neutrino
  masses and mixings (anarchy)
• Random 3 by 3 matrix
• MNS matrix distributed to the group invariant
  measure (Haba, HM)

P68
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Lower Bound on q13

• Anarchy predicts flat distribution in cos4q13
• 1D PKS 2(1cos4q13)sin22q13 for small q13
• Lower bounds
• sin22q13gt0.05 (95CL)
• sin22q13gt0.01 (99CL)

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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 m, t
• Normal or inverted hierarchy?
• Most symmetries predict the normal hierarchy
• CP Violation?
• Plausibility test of leptogenesis

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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

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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 evading
  m?eg, b?sg constraints
• (Chang, Masiero, HM)
• Expect CP violation in neutrino sector especially
  if leptogenesis (Rodejohann)

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Consequences in B physics

• Addtl contrib to Dms
• CP violation in Bs mixing (Bs?J/y f)

• Addtl CP violation in penguin b?s
• (Bd?f Ks)

Very reasonable place for new physics to show up!
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RR-dom case
also Uli Nierste in Heavy Flavour session
Harnik, Larson, HM, Pierce
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Conclusions

• Enormous progress in neutrino data
• Solar neutrino problem solved!
• Still some loose ends
• Many forthcoming experiments
• Three-generation oscillation very reasonable
• LSND still unclear
• Cosmological constraints beginning to be
  interesting
• Next key q13
• Long-baseline or reactor
• Neutrinos not stand alone
• Need info from high-energy frontier, quark sector
  to address the origin of masses and mixing

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Do We Need Theorists?