1. 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

2. 1. The Seesaw Mechanism

3. Minkowski; Yanagida; Gell-Man, Ramond and Slansky…

7. 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/ ];
M. Nebot et al., Zee Model arXiv: [hep-ph]].
R.~Franceschini et al.,Type-III [arXiv: [hep-ph]].
F.~del Aguila etal., Type I, II, III [arXiv: [hep-ph]].
P.~Fileviez Perez et al., Type-II [arXiv: [hep-ph]];
A.~Arhrib et al.,Type I+III Seesaw, arXiv: [hep-ph];
W.~Chao et al., Type I +II [arXiv: [hep-ph]];
X.-G. He et al., Type I and III, arXiv: [hep-ph]
X.-G. He and Ernest Ma, arXiv: [hep-ph]
T. Li and X.-G. He., Type III, arXiv: [hep-ph].

8. 2. Type II Seesaw at the LHC

9. Del Aguila and Aguilar-Saavedra

11. P. Perez et al.

14. 3. Small light and heavy mixing in Type I and III at the LHC Some features about Type I and III Seesaw Models

15. Type-I seesaw at LHC

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

17. Neutrino Mixing Schwetz et. al, Gonzalez-Garcia et. Al, Goswami et. al
Neutrino Mixing Schwetz et.al, Gonzalez-Garcia et. Al, Goswami et.al. Strumia et al.

18. Real angle wij -> small mixing solution
Real angle wij -> small mixing solution. Complex angle, can have large mixing solution.

20. Even with small V_{lN} Type-III seesaw can be tested at the LHC Tong Li and Xiao-Gang He, arXiv: [hep-ph]

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

43. Some sample solutions

45. 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!

46. If m_N < m_h, affect Higgs decay Br
If m_N < m_h, affect Higgs decay Br. Park, Wang and Yanagida, arXiv: ; Chen et al. arXiv:

47. Model realization for large light and heavy mixing X. -G. He and E
Model realization for large light and heavy mixing X.-G. He and E. Ma, arXiv: [hep-ph]

51. 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.