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Neutrino Seesaw Models at the LHC

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Neutrino Seesaw Models at the LHC

Xiao-Gang He

Department of Physics and Center for Theoretical Sciences

National Taiwan University

Talk at USTC, April 15

The Seesaw Mechanism

Type II Seesaw at the LHC

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

New possibility, large mixing, for Type-I and III seesaw at LHC

Conclusions

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

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

producing neutrino masses and mixing.

Production of new particles, the most direct test!

T.~Han and B.~Zhang, Heavy neutrino t LHC [arXiv:hep-ph/0604064];

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

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];

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 and Ernest Ma, arXiv:0907.2737[hep-ph]

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

4. New possibility, large mixing, for Type-I and III seesaw at LHCX.-G. He et al., arXiv:0907.1607[hep-ph] (earlier work: Smirnov and Kersten)

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!

For Type III Seesaw, no displayed vertex!

5. Conclusions

Seesaw models are the most economy models to produce naturally small

neutrino masses.

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

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

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

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

and be tested at the LHC.

Signature to distinguishing small and large mixing: displaced vertex for

Small mixing and no displaced vertex for large mixing.