Neutrinos and the Flavour
Puzzle: A Mini-Review
Stefan Antusch
University of Basel
Department of Physics
Review talk at EPS-HEP 2011
Max-Planck-Institut für Physik
(Werner-Heisenberg-Institut)
July 22, 2011
The Neutrino Flavour Puzzles
Neutrino masses:
Why so small?
How to extend the SM?
Lepton mixing:
Why so large? (TB?)
Stefan Antusch
2
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?
Such open questions are
great! It means we can still
make predictions ... !
Stefan Antusch
3
University of Basel & MPI of Physik (Munich)
The Neutrino Flavour Puzzle #1
Neutrino masses:
Why so small?
How to extend the SM?
Stefan Antusch
4
University of Basel & MPI of Physik (Munich)
... in model building, most approaches are based on:
ΣR
(type I or III)
m
MR
At which scale?
(A) At high scale (~ MGUT)
(B) At TeV scale (→ colliders, LHC)
(C) At eV energies (light sterile ν’s)
Stefan Antusch
5
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, ...
University of Basel & MPI of Physik (Munich)
?
... or something
completely different
R
m
Dirac neutrinos
MR
string theory
string theory
Stefan Antusch
6
University of Basel & MPI of Physik (Munich)
... to find answers we need to combine data from various sources:
indirect tests (e.g. LFV,
universality, non-unitarity)
Colliders (LHC)
Best chances for TeV
scale mass generation:
0νββ decay,
Tritium β decay,
cosmology
→ talk by Alessandro
Strumia (tomorrow)
Stefan Antusch
7
University of Basel & MPI of Physik (Munich)
The Neutrino Flavour Puzzle #2
Lepton mixing:
Why so large? (TB?)
Stefan Antusch
8
University of Basel & MPI of Physik (Munich)
I) Preliminary remark:
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):
S.A., Kersten, Lindner, Ratz (‘03)
Stefan Antusch
9
University of Basel & MPI of Physik (Munich)
I) “Direct” models:
Identify remnant symmetries!
GFam generated by S,T and U
→ S4 family symmetry
A4 possible as well
for certain selection
of field reps
GFam
Generator
T broken but
S,U preserved!
Neutrino
Sector
Generators
S, U broken but
T preserved!
Charged
Lepton
Sector
UTB
Altarelli, Feruglio, Ma, Hagedorn, Merlo, Luhn ...
Stefan Antusch
10
S4 preferred: Lam
University of Basel & MPI of Physik (Munich)
‘Direct’ vs. ‘indirect’ models:
King, Luhn (‘09)
II) “Indirect” models:
Dynamical fields
= Flavons ~ A, B, C
in 3 of GFam generate flavour
structure in the neutrino sector
GFam typically broken
completely in mν
→ vacuum alignment crucial
King, Ross, de Medeiros Varzielas, Malinsky, Chen, ...
Stefan Antusch
11
University of Basel & MPI of Physik (Munich)
Both approaches point to
non-Abelian discrete
family symmetries GFam!
Various successful models have been
constructed by many authors (too many
to review them all in a mini-review) ...!
Stefan Antusch
12
University of Basel & MPI of Physik (Munich)
→ talk by Michele Maltoni
Finally, if T2K gets
confirmed:
Is TB mixing
still the right LO
mixing pattern?
T2K collaboration (2011)
Stefan Antusch
→ talk by Claudio Gigante
13
University of Basel & MPI of Physik (Munich)
The flavour puzzle:
(At least) four aspects
Stefan Antusch
14
University of Basel & MPI of Physik (Munich)
We should not forget the other pieces
of the flavour puzzle!
I) The neutrino
flavour puzzle
II) The SM
flavour puzzle
IV) The puzzle of
CP violation
III) The “new physics”
flavour puzzle
Stefan Antusch
15
University of Basel & MPI of Physik (Munich)
Example from the SM flavour puzzle:
Why are the
masses of
down-type quarks
and charged
leptons so similar?
Stefan Antusch
16
University of Basel & MPI of Physik (Munich)
Example from the SM flavour puzzle
mb ↔ mτ ?
ms ↔ mμ ?
(running masses at the top-mass scale;
errors are 3 times the 1σ errors ...)
Stefan Antusch
17
University of Basel & MPI of Physik (Munich)
Mass relations are predictions of
unified models
[1] Georgi, Jarlskog (‘79)
[2] S.A., Spinrath (‘09)
[3] Allanach, King
(‘96)
[1]
[2]
[2]
[2]
[3]
[3]
In SUSY GUTs the viability
depends on SUSY parameters:
Stefan Antusch
→ testable @ colliders!
18
University of Basel & MPI of Physik (Munich)
Mu
Md
GUT
relation
e.g.: Uν+ = UTB
mν
Me
CP violation
 Consequencs: Lepton mixing sum rule relations, prediction for θ13,
predictions for the Dirac CP phase δMNS!
Stefan Antusch
19
University of Basel & MPI of Physik (Munich)
More generally in GUTs, when charged lepton corrections dominate ...
Mu
Md
GUT
relations
e.g.: Uν+ = UTB
mν
Me
Novel Clebsch factors for
viable GUT mass relations
→ can lead to large θ13MNS
(e.g. θ13MNS ≈ 7.6° or ≈
10°)
S.A., Maurer (’11)
1) Prediction for θ13MNS
(for
)
Stefan Antusch
20
University of Basel & MPI of Physik (Munich)
More generally in GUTs, when charged lepton corrections dominate ...
Mu
Md
GUT
relation
e.g.: Uν+ = UTB
mν
Me
2) Lepton mixing sum rule
(for
)
Stefan Antusch
King (’05); Masina (’05); S.A., King (‘05)
21
University of Basel & MPI of Physik (Munich)
→ δMNS ≈ 180°, θ13MNS≈ 10°
For large θ13MNS → δMNS ≈ 90°,270°
from S.A., Huber, King, Schwetz (’07)
2) Lepton mixing sum rule
(for
)
Stefan Antusch
22
University of Basel & MPI of Physik (Munich)
 GUT symmetries unify “vertically”, family symmetries unify
“horizontally”
GUTs x Family symmetries are
a poweful framework for
approaching the flavour puzzle!
Stefan Antusch
23
University of Basel & MPI of Physik (Munich)
The flavour puzzle with “new physics”
What is the flavour structure of the new
physics (if exists @ TeV energies)?
Stefan Antusch
24
University of Basel & MPI of Physik (Munich)
 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?
Stefan Antusch
25
University of Basel & MPI of Physik (Munich)
Family symmetries: Can solve SUSY flavour problem!
In particular: Non-Abelian family symmetries!
Abel, Khalil, Lebedev (’01)
Ross, Vives (‘02),
Ross, Velasco-Sevilla, Vives (‘04)
S.A., King, Malinsky (‘07)
...
•
Explain flavour structure in the SM, e.g.:
•
Generate flavour stucture of the SUSY particles:
SUSY flavour
structure related to
the one of the SM
Family
symmetry!
Stefan Antusch
Remaining tension can
be resolved in SUGRA:
S.A., King, Ross,
Malinsky (’08)
26
University of Basel & MPI of Physik (Munich)
Flavour physics effects = “DNA“
of flavour models
Altmannshofer, Buras,
Gori, Paradisi,
Straub (‘09)
Stefan Antusch
27
University of Basel & MPI of Physik (Munich)
The puzzle of CP violation
Why is the unitary
triangle right-angled?
Stefan Antusch
28
University of Basel & MPI of Physik (Munich)
 The unitarity triangle: Fit to the experimental data
Observation: The angle
α ≈ 90° ... just an
accident?
Stefan Antusch
29
University of Basel & MPI of Physik (Munich)
 The unitarity triangle: Fit to the experimental data
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)
Observation: The angle
α ≈ 90° ... just an
accident?
Stefan Antusch
→ poster by Martin Spinrath
30
University of Basel & MPI of Physik (Munich)
Challenge for flavour models: Resolve
all aspects of the flavour puzzle!
I) The neutrino
flavour puzzle
II) The SM
flavour puzzle
IV) The puzzle of
CP violation
III) The “new physics”
flavour puzzle
Stefan Antusch
31
University of Basel & MPI of Physik (Munich)
Thanks for
your attention!
Stefan Antusch
32
University of Basel & MPI of Physik (Munich)