Neutrinos and the Flavour Puzzle: A Mini-Review

Stefan Antusch

Max-Planck-Institut für Physik(Werner-Heisenberg-Institut)

University of BaselDepartment of Physics

July 22, 2011Review talk at EPS-HEP 2011

Stefan Antusch University of Basel & MPI of Physik (Munich)

The Neutrino Flavour Puzzles

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Neutrino masses:Why so small? How to extend the SM?

Lepton mixing:Why so large? (TB?)

Stefan Antusch University of Basel & MPI of Physik (Munich)

Many open neutrino questions …

What are the values of θ13, δ, sgn(Δm312)?

What is the absolute neutrino mass scale?

Are neutrino masses of Dirac or Majorana type?

If Majorana, what are the values of the Majorana phases?

Precise values of all leptonic mixing angles?

3

Such open questions are great! It means we can still make predictions ... !

Stefan Antusch University of Basel & MPI of Physik (Munich)

The Neutrino Flavour Puzzle #1

4

Neutrino masses:Why so small? How to extend the SM?

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mν

MR

ΣR

(type I or III)

Is it a tree-level “Seesaw”?P. Minkowski ('77), Mohapatra, Senjanovic, Yanagida, Gell-Mann, Ramond, Slansky, Schechter, Valle, Magg, Wetterich, Ma, Foot, Lew, He, Joshi, ...

(A) At high scale (~ MGUT)(B) At TeV scale (→ colliders, LHC)(C) At eV energies (light sterile ν’s)

... in model building, most approaches are based on:

At which scale?

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mν

MR

νR

Dirac neutrinos

string theory

string theory

?... or something

completely different

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... to find answers we need to combine data from various sources:

Colliders (LHC)

0νββ decay,Tritium β decay,cosmology

indirect tests (e.g. LFV,universality, non-unitarity)

→ talk by Alessandro Strumia (tomorrow)

Best chances for TeVscale mass generation:

Stefan Antusch University of Basel & MPI of Physik (Munich)

The Neutrino Flavour Puzzle #2

8

Lepton mixing:Why so large? (TB?)

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I) Preliminary remark:

S.A., Kersten, Lindner, Ratz (‘03)

Large mixing is no fixed point of the RG evolution → There is no unbroken symmetry to enforce TB mixing!

RGEs for the mixing angles (in LO):

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I) “Direct” models:Identify remnant symmetries!GFam generated by S,T and U→ S4 family symmetry

S4 preferred: Lam

A4 possible as wellfor certain selection of field reps

GFam

NeutrinoSector

Charged LeptonSectorUTB

Generator T broken but S,U preserved!

Generators S, U broken but T preserved!

Altarelli, Feruglio, Ma, Hagedorn, Merlo, Luhn ...

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II) “Indirect” models:

Dynamical fields = Flavons ~ A, B, Cin 3 of GFam generate flavour structure in the neutrino sector

GFam typically broken completely in mν

→ vacuum alignment crucial

‘Direct’ vs. ‘indirect’ models:King, Luhn (‘09)

King, Ross, de Medeiros Varzielas, Malinsky, Chen, ...

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Both approaches point to non-Abelian discrete

family symmetries GFam!

Various successful models have been constructed by many authors (too manyto review them all in a mini-review) ...!

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Finally, if T2K gets confirmed:

Is TB mixing still the right LO mixing pattern?

T2K collaboration (2011)

→ talk by Michele Maltoni

→ talk by Claudio Gigante

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The flavour puzzle:(At least) four aspects

Stefan Antusch University of Basel & MPI of Physik (Munich)

We should not forget the other pieces of the flavour puzzle!

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I) The neutrino flavour puzzle

III) The “new physics” flavour puzzle

II) The SM flavour puzzle

IV) The puzzle of CP violation

Stefan Antusch University of Basel & MPI of Physik (Munich)

Example from the SM flavour puzzle:

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Why are the masses of down-type quarks and charged leptons so similar?

Stefan Antusch University of Basel & MPI of Physik (Munich)

Example from the SM flavour puzzle

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(running masses at the top-mass scale; errors are 3 times the 1σ errors ...)

mb ↔ mτ ?

ms ↔ mμ ?

Stefan Antusch University of Basel & MPI of Physik (Munich)

Mass relations are predictions of unified models

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→ testable @ colliders!In SUSY GUTs the viability depends on SUSY parameters:

[2] S.A., Spinrath (‘09)[1] Georgi, Jarlskog (‘79) [3] Allanach, King (‘96)

[3]

[1]

[2]

[2][2]

[3]

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Mu

Me

Md

mν

GUT relation

CP violation

e.g.: Uν+ = UTB

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More generally in GUTs, when charged lepton corrections dominate ...

Mu

Me

Md

mν

GUT relationse.g.: Uν

+ = UTB

1) Prediction for θ13MNS

(for )

Novel Clebsch factors for viable GUT mass relations → can lead to large θ13

MNS (e.g. θ13

MNS ≈ 7.6° or ≈ 10°)S.A., Maurer (’11)

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More generally in GUTs, when charged lepton corrections dominate ...

Mu

Me

Md

mν

GUT relatione.g.: Uν

+ = UTB

2) Lepton mixing sum rule (for )

King (’05); Masina (’05); S.A., King (‘05)

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2) Lepton mixing sum rule (for )

from S.A., Huber, King, Schwetz (’07)

→ δMNS ≈ 180°, θ13MNS≈ 10° For large θ13

MNS → δMNS ≈ 90°,270°

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GUT symmetries unify “vertically”, family symmetries unify “horizontally”

GUTs x Family symmetries are a poweful framework for approaching the flavour puzzle!

Stefan Antusch University of Basel & MPI of Physik (Munich)

The flavour puzzle with “new physics”

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What is the flavour structure of the new physics (if exists @ TeV energies)?

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Supersymmetry: For each SM particle there is a supersymmetric “partner particle”. SUSY is broken: The SUSY particles have their own flavour structure

The flavour puzzle would get a “new dimension”: What is the flavour structure of the SUSY particles?

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• Explain flavour structure in the SM, e.g.:

• Generate flavour stucture of the SUSY particles:

Family symmetry!

SUSY flavour structure related to the one of the SM

Family symmetries: Can solve SUSY flavour problem!Abel, Khalil, Lebedev (’01)Ross, Vives (‘02),Ross, Velasco-Sevilla, Vives (‘04)S.A., King, Malinsky (‘07)...

Remaining tension can be resolved in SUGRA: S.A., King, Ross, Malinsky (’08)

In particular: Non-Abelian family symmetries!

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Fla

vour

phy

sics

effe

cts

= “

DN

A“

of fl

avou

r m

odel

sAltmanns-hofer, Buras,Gori, Paradisi,Straub (‘09)

Stefan Antusch University of Basel & MPI of Physik (Munich)

The puzzle of CP violation

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Why is the unitary triangle right-angled?

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The unitarity triangle: Fit to the experimental data

Observation: The angle α ≈ 90° ... just an accident?

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The unitarity triangle: Fit to the experimental data

Observation: The angle α ≈ 90° ... just an accident?

→ poster by Martin Spinrath

Recent development: New unified flavour models with GFam plus Z2 or Z4 shaping symmetries (& spont. CP viol.): → can explain α = 90° by realising the “phase sum rule”→ δMNS {0°,90°,180°,270°} ∈S.A., King, Luhn, Spinrath (‘11)

Stefan Antusch University of Basel & MPI of Physik (Munich)

Challenge for flavour models: Resolve all aspects of the flavour puzzle!

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I) The neutrino flavour puzzle

III) The “new physics” flavour puzzle

II) The SM flavour puzzle

IV) The puzzle of CP violation

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Thanks for your attention!