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Neutrino physics Lecture 2: Theory of neutrino mass, and physics BSM?

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Neutrino physicsLecture 2: Theory of neutrino mass, and physics BSM?

Herbstschule für Hochenergiephysik

Maria Laach

04-14.09.2012

Walter Winter

Universität Würzburg

TexPoint fonts used in EMF: AAAAAAAA

- Measuring neutrino mass
- The seesaw paradigm
- Neutrino mass models at the TeV scale:What ingredients do “natural” models need?
- Is it possible that new physics shows up in the neutrino sector only?
- How does the large q13 affect our understanding of (lepton) flavor?
- Summary and conclusions

Measuring neutrino mass

- Direct test of neutrino mass by decay kinematics
- Current bound: 1/250.000 x me (2 eV) TINY!
- Future experiment: KATRIN (Karlsruhe Tritium Neutrino Experiment)1/2.500.000 x me (0.2 eV)

~8800 km

(Guido Drexlin, NOW 2008)

e-

W-

n

p

- Two times simple beta decay:
- Neutrinoless double beta decay:

e-

e-

2 x n2 x e

W-

W-

n

n

p

p

e-

=

Caveat: discovering 0nbb does not mean that one has actually seen Majorana neutrinos!

0 x n2 x e

W-

n

p

- Example:Relativistic neutrinos damp the formation of structure
- Essentially sensitive to sum of neutrino masses
- Information from different cosmological datasets used in literature
- Limit ~ eV

(S. Hannestad)

… might finally be used rule to out that neutrino physics in charge of 0nbb!

The seesaw paradigm

- Why are the neutrinos morethan 250.000 times lighter than the electron?
- Cannot be described in simple extensions of the Standard Model
- Is the neutrino mass the lowest order perturbation of physics BSM?

- Seesaw mechanism: Neutrino mass suppressed by heavy partner, which only exists in the early universe (GUT seesaw)?
- Decay of MR origin of matter-antimatter-asymmetry?
- CP violation? Test in neutrino oscillations!
- Requires Majorana nature of neutrino!Test in neutrinoless double beta decay (0nbb)

Other SM particles

Heavy partner

BSM physics described by effective operators in the low-E limit (gauge invariant):

L: Scaleof new physics

Neutrinomass(LNV)

Leptonflavorviolation (LFV)

But these are no fundamental theories (non-renormalizable operators). Idea: Investigate fundamental theories (TeV completions) systematically!

- Neutrino mass from d=5 (Weinberg) - Operator
- Fundamental theories at tree level:
- Neutrino mass ~ Y2 v2/L (type I, III see-saw)
- For Y = O(1), v ~ 100 GeV: L ~ GUT scale
- For L ~ TeV scale: Y << 10-5
- Interactions difficult to observe at LHC
- Couplings “unnaturally“ small?

H

H

?

Type II

Type III

Seesaw

Type I

L

L

Neutrino masses at the TeV scale?

… and physics at the LHC …

- Goals:
- New physics scale “naturally“ at TeV scale(i.e., TeV scale not put in by hand) Testable at the LHC?!
- Yukawa couplings of order one

- Requires additional suppression mechanisms. The typical ones:
- Radiative generation of neutrino mass (n loops)
- Neutrino mass from higher than d=5 effective operator
- Small lepton number violating contribution e (e.g. inverse see-saw, RPV SUSY models, …)

(Florian [email protected] Florence 2012)

Loop suppression, controlled by 1/(16 p2)

Type I, II, IIseesaw

Depends onmediators/int.

Zee, 1980;Ma, 1998; …

Tree

1-loop

2-loop

d=5

Discrete symmetryto forbid d=5?

Depends on scale:L > 4pv ~ 3 TeV?

d=7

Suppression by d, controlled by 1/L2

d=8

d=11

How can I make sure that no lower order operators are generated?

- Approach: Use higher dimensional operators, e.g.
- Leads to
- Estimate: for L ~ 1 – 10 TeV and mn linear in Yukawas (worst case):
- d = 9 sufficient if no other suppression mechanism
- d = 7 sufficient if Yukawas ~ me/v ~ 10-6 allowed

H

H

- Loop d=5 contribution dominates for or L > 3 TeV
- Conclusion: If assumed that d=7 leading, one effectively has to put L << 3 TeV by hand(see e.g. Babu, Nandi, Tavartkiladze, 2009)
- Can one avoid this?

H

H

H

H

Close loop

L

L

L

L

H+

d=5 operator

d=7 operator

- Define genuine d=D operator as leading contribution to neutrino mass with all operators d<D forbidden
- Use new U(1) or discrete symmetry (“matter parity“)
- Problem: H+H can never be charged under the new symmetry! Need new fields!
- The simplest possibilities are probably(e.g. Chen, de Gouvea, Dobrescu, hep-ph/0612017; Godoladze, Okada, Shafi, arXiv:0809.0703)(e.g. Babu, Nandi, hep-ph/9907213; Giudice, Lebedec, arXiv:0804.1753)

Bonnet, Hernandez, Ota, Winter, JHEP 10 (2009) 076

- Simplest possibility (d=7): Z5 with e.g.(SUSY: Z3)

SUSY:only this one(but: there canbe operators withthe scalar singletin the NMSSM)

Same for d=9

Bonnet, Hernandez, Ota, Winter, JHEP 10 (2009) 076

- Systematically decompose d=7 operator in all possible ways
- Notation for mediators:

Lorentz

SU(2)

Y=Q-I3

Bonnet, Hernandez, Ota, Winter, JHEP 10 (2009) 076

- Generalizations of originial see-saws: Duplication of the original see-saws plus scalars
- Type I (fermionic singlet)
- Type II(scalar triplet)
- Type III(fermionic triplet)Characteristics:Similar phenomenology!

Krauss, Ota, Porod, Winter, Phys. Rev. D84 (2011) 115023

- Neutral fermion mass matrix after EWSB in basis

2

Flavor struct. by

3

2

1

1

Mass states: ni

Fermionic doublets#17 from list

Compare to “inverse see-saw“(suppression mechanism 3)if heavy doublets integrated out

Krauss, Ota, Porod, Winter, Phys. Rev. D84 (2011) 115023

- Test mediators
- Test LFV
- Test LNV

compare

Bonnet, Hernandez, Ota, Winter, JHEP 10 (2009) 076

Loop suppression, controlled by 1/(16 p2)

Tree

1-loop

2-loop

Switched off by discrete symmetry

Switched off bydiscrete symmetry

d=5

Strategies for higher loops:Farzan, Pascoli, Schmidt, arXiv:1208.2732

To beavoided

d=7

Suppression by d, controlled by 1/L2

d=8

for L < 3 TeV

d=11

Example 1: d=9 at tree level

Physics at TeV scale with O(1) couplings

Example 2: d=7 at two loop Suppression mechanisms 1), 2), and 3)

New physics in neutrino sector only?

Most discussed options in literature:

Light sterile neutrinos (aka: light SM singlets)

Heavy SM singlets ( non-unitary mixings)

Non-standard interactions (aka: flavor changing neutral currents)

- LSND/MiniBooNE
- Reactor+gallium anomalies
- Global fits

(MiniBooNE @ Neutrino 2012)

(B. Fleming, TAUP 2011)

(Kopp, Maltoni, Schwetz, 1103.4570)

- Well known tension between appearance and disapp. data (appearance disappearance in both channels)
- Need one or more new experiments which can test
- ne disappearance (Gallium, reactor anomalies)
- nm disappearance (overconstrains 3+N frameworks)
- ne-nm oscillations (LSND, MiniBooNE)
- Neutrinos and antineutrinos separately (CP violation? Gallium vs reactor?)

- Example: nuSTORM - Neutrinos from STORed Muons(LOI: arXiv:1206.0294) Summary of options: Appendix of white paper arXiv:1204.5379

also: “MUV“

- Integrating out heavy fermion fields (such as in a type-I TeV see-saw), one obtains neutrino mass and the d=6 operator (here: fermion singlets)
- Re-diagonalizing and re-normalizing the kinetic terms of the neutrinos, one has
- This can be described by an effective (non-unitary) mixing matrix e with N=(1+e) U
- Relatively stroung bounds already, perhaps not so good candidate for future measurements(see e. g. Antusch, Baumann, Fernandez-Martinez, arXiv:0807.1003)

- Typically described by effective four fermion interactions (here with leptons)
- May lead to matter NSI (for g=d=e)
- May also lead to source/detector NSI

How plausible is a modelleading to such NSI(and showing up inneutrino sector only)?

- Charged leptonflavor violation
- Strongbounds

Ex.:

NSI

4n-NSI

CLFV

e

m

ne

nm

ne

nm

ne

ne

e

e

e

e

- Non-standard neutrino interact.
- Effects in neutrino oscillations in matter

- Non-standard int. with 4n
- Effects in environments with high neutrino densities (supernovae)

BUT: These phenomena are not independent (SU(2) gauge invariance!)Is it possible that new physics is present in the neutrino sector only?

Davidson, Pena-Garay, Rius, Santamaria, 2003

- Decouple CLFV and NSI by SU(2) symmetry breaking with operator
- Works at effective operator level, but are there theories allowing that? [at tree level]

Project outneutrino field

Project outneutrino field

Feynman diagrams

Basis (Berezhiani, Rossi, 2001)

- Decompose all d=8 leptonic operators systematically
- The bounds on individual operators from non-unitarity, EWPT, … are very strong! (Antusch, Baumann, Fernandez-Martinez, arXiv:0807.1003)

- Need at least two mediator fields plus a number of cancellation conditions(Gavela, Hernandez, Ota, Winter, Phys. Rev. D79 (2009) 013007)

Avoid CLFVat d=8:C1LEH=C3LEH

Combinedifferentbasis elements C1LEH, C3LEH

Canceld=8CLFV

But these mediators cause d=6 effects Additional cancellation condition(Buchmüller/Wyler – basis)

Implications of large q13: flavor

Block diag.

Charged leptonmass terms

Eff. neutrinomass terms

cf., charged current

Rotates left-handed fields

- Tri-bimaximal mixings probably most discussed approach for neutrinos (Ul often diagonal)
- Can be obtained in flavor symmetry models (e.g., A4, S4)
- Consequence: q13=0 Obviously not!
- Ways out for large q13?

q13

?

very small

very large

Structure:A4, S4, TBM, …

Anarchy:Random draw?

vs.

Some structure + randomness:Froggatt-Nielsen?

Corrections?CL sector?RGR running?

e.g. q12 = 35 + q13cosd(Antusch, King)

Quark-leptoncompementarity:q13 ~ qC?

Different flavor symmetry?

- Idea: perhaps the mixing parameters are a “random draw“?
- Challenge: define parameterization-independent measure
- Result: large q13 “natural“, no magic needed

(Hall, Murayama, Weiner, 2000; de Gouvea, Murayama, 2003, 2012)

(F. Plentinger)

- YL/R are SM fermions
- After integrating out the heavy fermions:
- Integer power n is controlled by the (generation/flavor-dependent) quantum numbers of the fermions under the flavor symmetry
- K: (complex) generation dependent (random) order one coefficients
- Well-suited to describe hierarchies

Example:

Ml~

Meloni, Plentinger, Winter, PLB 699 (2011) 244

Charged leptons:Strong hierarchy,masses throughSM Yukawas Quarks:Strong hierarchiesSmall mixings

Neutrinos:Mild (no?) hierarchy,large mixings, Majorana masses? Origin:physics BSM?LNV operator?

q13=0

Ansatz suitablefor hierarchies,such as Froggatt-Nielsen?

Flavor symmetry,structure?Tri-bimaximal mixing“paradigm“?

- Can control the size of q13 by suitable U(1) charges/mass texture for the charged lepton sector:
- Challenge:
- Deviations from TBM q12 typically accompanied by large q13
- Re-think zeroth order paradigm (TBM)???

Meloni, Plentinger, Winter, PLB 699 (2011) 244

- Are neutrinos masses evidence for physics BSM?
- Neutrinoless double beta decay
- Tests at the LHC

- 0nbb signal + CPV in lepton sector + no evidence for n mass at the LHC
- GUT seesaw, leptogenesis?

- Natural TeV neutrino mass model requires additional suppression mechanism; then, however, plausible to discover it at the LHC
- Most likely case for new physics in neutrino sector: fourth generation (light sterile neutrino)?
- Theory of flavor has to be re-thought after q13 discovery