Seesaw at the LHC Seesaw at the LHC

Xiao-Gang HeXiao-Gang He

CHEP, PUK and CTS, NTUCHEP, PUK and CTS, NTU

1. Theoretical models for small neutrino masses1. Theoretical models for small neutrino masses

2. Type II seesaw at the LHC2. Type II seesaw at the LHC

3. Type I and III: Small light and heavy neutrino mixing at the LHC3. Type I and III: Small light and heavy neutrino mixing at the LHC

4. New possibility for Type-I and III seesaw at LHC4. New possibility for Type-I and III seesaw at LHC

5. Model realization for large light and heavy mixing5. Model realization for large light and heavy mixing

6. Conclusions6. Conclusions

1. Theoretical models for small neutrino masses1. Theoretical models for small neutrino masses

Some theoretical models for neutrino massesSome theoretical models for neutrino masses

Loop generated neutrino masses: The Zee ModelLoop generated neutrino masses: The Zee Model(Zee, PLB, 1980)(Zee, PLB, 1980)

Add: h (1,1)(1) scalar (a,b)(c) SU(3)xSU(2)xU(1) numbersAdd: h (1,1)(1) scalar (a,b)(c) SU(3)xSU(2)xU(1) numbers

Replace one Higgs double by two: phi^{1,2}Replace one Higgs double by two: phi^{1,2}

No tree level neutrino mass term! At one loop:No tree level neutrino mass term! At one loop:

Simplest Zee model: f_2 = 0Simplest Zee model: f_2 = 0

Ruled out by present data.Ruled out by present data. (X.-G. He, EPJC, 2003) (X.-G. He, EPJC, 2003)

With f_2 non-zero. Can be consistent with data.With f_2 non-zero. Can be consistent with data.

2. Type II Seesaw at the LHC2. Type II Seesaw at the LHC

P.~Fileviez Perez et al., Type-II [arXiv:0805.3536 [hep-ph]];P.~Fileviez Perez et al., Type-II [arXiv:0805.3536 [hep-ph]];

Del Aguila and Aguilar-SaavedraDel Aguila and Aguilar-Saavedra

P. Perez et al.P. Perez et al.

3. Type I and III: Small light and heavy neutrino mixing at 3. Type I and III: Small light and heavy neutrino mixing at the LHC the LHC

What LHC can do for neutrino physics? A lot. One What LHC can do for neutrino physics? A lot. One

of them is to probe heavy degree of freedom in models of them is to probe heavy degree of freedom in models

producing neutrino masses and mixing. producing neutrino masses and mixing.

Production of new particles, the most direct test!Production of new particles, the most direct test!T.~Han and B.~Zhang, Heavy neutrino t LHC [arXiv:hep-ph/0604064];T.~Han and B.~Zhang, Heavy neutrino t LHC [arXiv:hep-ph/0604064];

M. Nebot et al., Zee Model arXiv:0711.0483 [hep-ph]]. M. Nebot et al., Zee Model arXiv:0711.0483 [hep-ph]].

R.~Franceschini et al.,Type-III [arXiv:0805.1613 [hep-ph]].R.~Franceschini et al.,Type-III [arXiv:0805.1613 [hep-ph]].

F.~del Aguila etal., Type I, II, III [arXiv:0808.2468 [hep-ph]].F.~del Aguila etal., Type I, II, III [arXiv:0808.2468 [hep-ph]].

A.~Arhrib et al.,Type I+III Seesaw, arXiv:0904.2390 [hep-ph];A.~Arhrib et al.,Type I+III Seesaw, arXiv:0904.2390 [hep-ph];

W.~Chao et al., Type I +II [arXiv:0804.1265 [hep-ph]];W.~Chao et al., Type I +II [arXiv:0804.1265 [hep-ph]];

X.-G. He et al., Type I and III, arXiv: 0908.1607[hep-ph]X.-G. He et al., Type I and III, arXiv: 0908.1607[hep-ph]

X.-G. He and Ernest Ma, arXiv:0907.2737[hep-ph]X.-G. He and Ernest Ma, arXiv:0907.2737[hep-ph]

T. Li and X.-G. He., Type III, arXiv:0907.4193[hep-ph].T. Li and X.-G. He., Type III, arXiv:0907.4193[hep-ph].

Some features about Type I and III Seesaw ModelsSome features about Type I and III Seesaw Models

Type-I seesaw at LHCType-I seesaw at LHC

V_{lN} ~ (m_\nu/m_N)^{1/2} < 10^{-6} for one generation. Too small!V_{lN} ~ (m_\nu/m_N)^{1/2} < 10^{-6} for one generation. Too small!

There are exceptions to the “general solution”There are exceptions to the “general solution”

Even with small V_{lN} Type-III seesaw can be tested at the LHCEven with small V_{lN} Type-III seesaw can be tested at the LHC

Tong Li and Xiao-Gang He, arXiv:0907.4193[hep-ph]Tong Li and Xiao-Gang He, arXiv:0907.4193[hep-ph]

4. New possibility for Type-I and III seesaw at LHC4. New possibility for Type-I and III seesaw at LHC

X.-G. He et al., arXiv:0907.1607[hep-ph]X.-G. He et al., arXiv:0907.1607[hep-ph]

Some sample solutionsSome sample solutions

For U_{\nu U} of order 0.03, the cross section can be as large as 1 fb for m_N For U_{\nu U} of order 0.03, the cross section can be as large as 1 fb for m_N

up to 150 GeV. Not hopelessly small!up to 150 GeV. Not hopelessly small!

5. Model realization for large light and heavy mixing5. Model realization for large light and heavy mixingX.-G. He and E. Ma, arXiv:0907.2737[hep-ph]X.-G. He and E. Ma, arXiv:0907.2737[hep-ph]

6. Conclusions6. Conclusions

One can have theoretical models in which the elements in U_{\nu N} One can have theoretical models in which the elements in U_{\nu N}

can be as large as a few percent.can be as large as a few percent.

For the single N (Type-I, III) and E (Type-III) production, the cross For the single N (Type-I, III) and E (Type-III) production, the cross

section can be as large as 1 fb with masses as heavy as 150 GeV.section can be as large as 1 fb with masses as heavy as 150 GeV.

No displaced vertex in the large mixing case. Decay pattern very No displaced vertex in the large mixing case. Decay pattern very

different from the small mixing solutions discussed earlier.different from the small mixing solutions discussed earlier.

For Type III seesaw, heavy leptons can be probed up to 1 TeV at the For Type III seesaw, heavy leptons can be probed up to 1 TeV at the

LHC.LHC.

There are chances that underlying theory for neutrino mass and mixing There are chances that underlying theory for neutrino mass and mixing

be tested at the LHC. Plus other new experiments on neutrinos going to be tested at the LHC. Plus other new experiments on neutrinos going to

operation soon, more information about neutrinos will come.operation soon, more information about neutrinos will come.

Other interesting things related to neutrino physicsOther interesting things related to neutrino physics

Neutrino properties may also hold the key to many cosmological Neutrino properties may also hold the key to many cosmological

problems, such as leptogenesis can explain why our universe is matter problems, such as leptogenesis can explain why our universe is matter

dominated one. If through seesaw models, the heavy neutrinos can be dominated one. If through seesaw models, the heavy neutrinos can be

a slow as TeV scale.a slow as TeV scale.

More flavor physics: mu -> e gamma, mu -> eee, e - \mu conversionMore flavor physics: mu -> e gamma, mu -> eee, e - \mu conversion

Neutrino oscillations, mass measurement s: Dirac or Majorana, CPV or Neutrino oscillations, mass measurement s: Dirac or Majorana, CPV or

CPC ……CPC ……

Much can be done with other facilities too. Together with LHCMuch can be done with other facilities too. Together with LHC

An exciting LHC era is ahead of us!An exciting LHC era is ahead of us!