Can we distinguish among different models for mass in the near future? Carla Biggio...

Can we distinguish among different models for mass

in the near future?

Carla BiggioMax-Planck-Institut für Physik, München,

Germany

Convegno informale di fisica teorica – Sestri Levante 2008

Based on collaborations with:

A. Abada, S. Antusch, F. Bonnet, E. Fernández-Martínez,

B. Gavela, T. Hambye, J. López-Pavón

Sestri Levante 08Carla Biggio, MPI, Germany

The “problem” of masses in 6 lines…

• are exactly massless in the Standard Model (SM)

• Experimentally: they oscillate → they are massive there is leptonic flavour mixing

• m« ml : m< O(eV)

→ we need new physics (NP) beyond the SM to describe their masses

→ we’d like this new physics to explain their smallness

232252 10 10 eVmeVm atmsun





• m« ml : m< O(eV)




Explaining the smallness of masses with new physics at high energy: → the seesaw mechanism





• m« ml : m< O(eV)




The “bansigo” mechanism…

Explaining the smallness of masses with new physics at high energy: → the seesaw mechanism


Effective field theory approachthe effects of high energy NP @ low energy encoded in higher dimensional operators

...62

65

5

dd

dd

SMeff OM

kO

M

kLL


Effective field theory approachthe effects of high energy NP @ low energy encoded in higher dimensional operators

...62

65

5

dd

dd

SMeff OM

kO

M

kLL

Many Od>4 op.s with SM fields but Od=5 is UNIQUE!

5dc


Effective field theory approach

D=5 operator violates lepton number → must be Majorana

depends on the model ~O(1) , M~MGUT , v=vEW → m~10-3

→

v v

the effects of high energy NP @ low energy encoded in higher dimensional operators

...62

65

5

dd

dd

SMeff OM

kO

M

kLL


5dc


Effective field theory approach

D=5 operator violates lepton number → must be Majorana

depends on the model ~O(1) , M~MGUT , v=vEW → m~10-3

→

v v

the effects of high energy NP @ low energy encoded in higher dimensional operators

...62

65

5

dd

dd

SMeff OM

kO

M

kLL


In how many ways can I obtain this Od=5?

5dc


Tree-level realisations of seesaw mechanism

Type I See-SawNR fermionic singlet

Minkowski, Gell-Mann, Ramond,Slansky, Yanagida, Glashow, Mohapatra, Senjanovic, …




Type II See-Saw scalar triplet


Magg, Wetterich, Lazarides,Shafi, Mohapatra, Senjanovic, Schecter, Valle, …





Type III See-SawR fermionic triplet



Foot, Lew, He, Joshi, Ma, Roy, …, Bajc, Nemevsek, Senjanovic, Dorsner, Fileviez-Perez





Type III See-SawR fermionic triplet


Linearly prop to Y

suppressed by /M2


Foot, Lew, He, Joshi, Ma, Roy, …, Bajc, Nemevsek, Senjanovic, Dorsner, Fileviez-Perez


How can we distinguish among them?


How can we distinguish among them?

• not from the d=5 operator: it’s the same!

• either we are able to produce heavy states

or

from the d=6 operator

→ which are the d=6 operators associated to these seesaw models?


D=6 operators

Broncano, Gavela,Jenkins 02

Type I:


D=6 operators


Type I:

Type III:Abada, CB, Bonnet,Gavela, Hambye 07


D=6 operators


Type I:

Type III:

Type II:

Abada, CB, Bonnet,Gavela, Hambye 07

Abada, CB,Bonnet,Gavela,Hambye 07

It is not suppressed by


D=6 operators


Type I:

Type III:

Type II:D=6 operatorsdo not violate Lepton Number

It is not suppressed by




Phenomenological effects

Type I:• non-unitary mixing in CC• FCNC for

Broncano, Gavela, Jenkins 02Antusch, CB, F.dez-M.nez, Gavela, López-Pavón 06


(D=6 op and non-unitarity in type I seesaw)

Kinetic terms → diagonalized and normalized → unitary transf. + rescaling

mab → diagonalized → unitary transformation U

N is not unitary

PMNSUN

21

(O())

Antusch, CB, F.dez-M.nez, Gavela, López-Pavón 06



Type I:

Type III:

• non-unitary mixing in CC• FCNC for

• non-unitary mixing in CC• FCNC for • FCNC for charged leptons





Type I:

Type III:

Type II:

• LFV 4-fermions interactions







Can we really use d=6 ops to distinguish?



Generically if Y≈O(1) → cd=6 ≈ (cd=5)2 → very suppressed

YMYc Td 15 YMYcd 2†6 (fermionic)




YMYc Td 15 YMYcd 2†6

Is it possible to have a LARGE effect coming from cd=6

still with SMALL cd=5 ( mass) without fine-tuning?

(fermionic)




We need to decouple d=5 op. from d=6

YMYc Td 15 YMYcd 2†6

Is it possible to have a LARGE effect coming from cd=6

still with SMALL cd=5 ( mass) without fine-tuning?

- d=5 operator violates lepton number- d=6 operators conserve it

→ natural from the point of view of symmetries…

(fermionic)


Direct Lepton Number Violation Scheme

assume L-conserving setup with small M (M~1TeV) and large Y (Y~O(1)):

large

L conserved





large

L conserved

assume L broken by small perturbation :

Neutrino mass directly proportionalto a small source of L violation rather than inversely proportionalto a large one





large

L conserved

assume L broken by small perturbation :

Neutrino mass directly proportionalto a small source of L violation rather than inversely proportionalto a large one

Is this possible?



Seesaw at low scale

YM2

cd=5 ≈ Y †YM2

cd=6 ≈• Type II seesaw:


Seesaw at low scale

YM2

cd=5 ≈ Y †YM2

cd=6 ≈

000

022

02

00

02

00

1211

12

11

M

Mv

Yv

Y

vY

vY

González-García, Valle 89…Kersten, Smirnov 07

• Inverse/Double type I (III) seesaw:

Ex.) 2 generations (L, L, Nc1R, Nc

2R):

• Type II seesaw:

If Y~O(1) and M~1TeV → large cd=6

L is conserved → m=0



Seesaw at low scale

YM2

cd=5 ≈ Y †YM2

cd=6 ≈

M

Mv

Yv

Y

vY

vY

00

022

02

00

02

00

1211

12

11




2R):

• Type II seesaw:


L is broken by → YM

Ym T2



Seesaw at low scale

YM2

cd=5 ≈ Y †YM2

cd=6 ≈

M

Mv

Yv

Y

vY

vY

00

022

02

00

02

00

1211

12

11




2R):

• Type II seesaw:


L is broken by → YM

Ym T2

Direct Lepton Number Violation can be realised in any seesaw model→ low scale seesaw is possible and its effects can be observed in the near future



Testing the seesaws…

Type II: LFV 4-fermions interactions→eee, →lll, →e, →l

bounds on variouscombinations of 2

2

M

Y

Scalar seesaw:





2

M

Y

Scalar seesaw:

Fermionic seesaws:

non-unitarity

3x3

non-unitary

unitary





2

M

Y

Scalar seesaw:

Fermionic seesaws:

non-unitarity


†NNCC

SMCC analogous for NC

•W, Z, (semi)leptonic decays → (NN†)

• unsuppressed →e, →l→ (NN†)





2

M

Y

Scalar seesaw:

Fermionic seesaws:

non-unitarity

Type I:

Type III:



†NNCC

SMCC analogous for NC

•W, Z, (semi)leptonic decays → (NN†)

• unsuppressed →e, →l→ (NN†)

Similar to type I but→eee, →lll at tree-level→ stronger bounds


Bounds on (Y†Y/M2) in type II

• Upper bounds from LFV 4-fermions processes: indep. of

or stronger

Partly from:Barger et al. 82, Pal 83,Bernabeu et al. 84, 86,Bilenky, Petcov 87,Gunion et al. 89, 06,Mohapatra 92



Bounds on (Y†Y/M2) in type II

• Upper bounds from LFV 4-fermions processes: indep. of

or stronger

Partly from:Barger et al. 82, Pal 83,Bernabeu et al. 84, 86,Bilenky, Petcov 87,Gunion et al. 89, 06,Mohapatra 92


Best signature of thismodel at LHC: dileptons

Kadastic, Raidal, Rebane 07,Garayoa, Schwetz 07, …


Bounds on (Y†Y/M2) in type I and III

• No deviations from unitarity measured so far → only upper bounds

TYPE I

TYPE III

Bounds are a bit stronger for type III.In particular we have better bounds on off-diag elements due to tree-level →eeeand →3l due to FCNC for charged leptons

General trend:

or smaller

Abada, CB, Bonnet, Gavela, Hambye 07

Antusch, CB, F.dez-M.nez, Gavela, López-Pavón 06


→e and →l in type III@ O() and M>>MW

YMYv 2†

2

2

Observation of radiative decays and no tree level decays→ the type III seesaw cannot be the only source of lepton flavour violating new physics

• worst bounds with respect to tree-level decays l→3l; But:

Abada, CB, Bonnet, Gavela, Hambye 08


ConclusionsCan we distinguish among different models for mass in the near future?


ConclusionsCan we distinguish among different models for mass in the near future?

YES, IF… …if the new physics scale is low enough…


Conclusions

• d=6 effective operators crucial to distinguish among different models

Can we distinguish among different models for mass in the near future?

YES, IF… …if the new physics scale is low enough


Conclusions


• d=6 ops are usually suppressed but not necessarily:




Conclusions



Direct Lepton Violation pattern: d=5 op. suppressed by small scale d=6 ops. unsuppressed




Conclusions




this pattern is the same in all models: natural in the scalar case, inverse seesaw for fermionic seesaws




Conclusions




this pattern is the same in all models: natural in the scalar case, inverse seesaw for fermionic seesaws • rich phenomenology associated to low scale seesaws:




Conclusions





- provides bounds on high energy theory parameters




Conclusions





- provides bounds on high energy theory parameters

- stay tuned!!! Maybe interesting results in the near future…



Can we distinguish among different models for mass in the near future? Carla Biggio...

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