Seesaw at the LHC Seesaw at the LHC

Xiao-Gang HeXiao-Gang HeDepartment of Physics and Center for Theoretical SciencesDepartment of Physics and Center for Theoretical Sciences

National Taiwan UniversityNational Taiwan University

1.1.Seesaw for small neutrino massesSeesaw for small neutrino masses

2.2.Type II Seesaw at the LHCType II Seesaw at the LHC

3.3.Small light and heavy mixing in Type I and III at the LHCSmall light and heavy mixing in Type I and III at the LHC

4.4.New possibility for Type-I and III seesaw at LHCNew possibility for Type-I and III seesaw at LHC

5.5.ConclusionsConclusions

1. Seesaw for small neutrino masses1. Seesaw for small neutrino masses

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 the heavy degree of freedom in models of them is to probe the 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]].

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

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

Del Aguila and Aguilar-SaavedraDel Aguila and Aguilar-Saavedra

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

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

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!

Neutrino MixingNeutrino MixingSchwetz et.al, Gonzalez-Garcia et. Al, Goswami et.al. Strumia et al.Schwetz et.al, Gonzalez-Garcia et. Al, Goswami et.al. Strumia et al.

Real angleReal angle w wij ij -> small mixing solution. -> small mixing solution. Complex angle, can have large mixing solution.Complex angle, can have large mixing 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] (earlier work: Smirnov and Kerstin)(earlier work: Smirnov and Kerstin)

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!

Model realization for large light and heavy mixingModel 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]

5. Conclusions5. Conclusions

Seesaw models are the most economy models to produce naturally small Seesaw models are the most economy models to produce naturally small

neutrino masses.neutrino masses.

If the seesaw scale is of order a TeV, LHC may be able to directly If the seesaw scale is of order a TeV, LHC may be able to directly

produce the heavy degrees of freedom (pair producing) providing direct produce the heavy degrees of freedom (pair producing) providing direct

test for type II and type III (small light and heavy neutrino mixing) models.test for type II and type III (small light and heavy neutrino mixing) models.

There are solutions with sizeable mixing between light and heavy There are solutions with sizeable mixing between light and heavy

neutrinos. In this case the single N (Type-I, III) and E (Type-III) production neutrinos. In this case the single N (Type-I, III) and E (Type-III) production

cross sections can be as large as 1 fb with masses as heavy as 150 GeV cross sections can be as large as 1 fb with masses as heavy as 150 GeV

and be tested at the LHC. and be tested at the LHC.

Signature to distinguishing small and large mixing: displaced vertex for Signature to distinguishing small and large mixing: displaced vertex for

Small mixing and no displaced vertex for large mixing.Small mixing and no displaced vertex for large mixing.