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TeV-scale seesaw with non-negligible left-right neutrino mixings

TeV-scale seesaw with non-negligible left-right neutrino mixings . Yukihiro Mimura (National Taiwan University). Based on arXiv:1110.2252 [hep-ph]. Collaboration with N. Haba , T. Horita , and K. Kaneta (Osaka U). Seminar at Academia Sinica (2012.1.13, Friday). Introduction.

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TeV-scale seesaw with non-negligible left-right neutrino mixings

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  1. TeV-scale seesaw with non-negligible left-right neutrino mixings Yukihiro Mimura (National Taiwan University) Based on arXiv:1110.2252 [hep-ph] Collaboration with N. Haba, T. Horita, and K. Kaneta (Osaka U) Seminar at Academia Sinica (2012.1.13, Friday)

  2. Introduction Neutrinos are massive, but active neutrino masses are tiny, < O(1) eV The simplest mechanism is type-I seesaw. “Natural” scale for

  3. Q. Is there a chance to “observe” the right-handed neutrino? Ex. C.f. Right-handed neutrino mass can be O(100) GeV, but, …..

  4. Left-right neutrino mixing: Ex. Negligibly small to create the Majorana neutrino at the collider.

  5. Q. Is it possible to make the left-right mixing large enough to detect the existence of the right-handed neutrino? A. Yes, if generation structure is taken into account. Buchmuller-Wyler, Buchmuller-Greub, Tommasini-Barenboim-Bernabeu-Jarskog,Gluza, Kerstern-Smirnov, Adhikari-Raychaudhuri,Ma, He-Ma, He-Oh-Tandean-Wen, Chen-He-Tandean-Tsai, …. (sorry, incomplete list)

  6. What we have done: Find a convenient flavor basis to describe the non-negligible left-right neutrino mixing. Consider a flavor symmetry to obtaina sizable left-right neutrino mixing. Experimental implication

  7. What we see in this talk: Introduction (Done) Convenient basis to describe theleft-right neutrino mixing Experimental constraints Flavor symmetry Experimental implications Summary

  8. = Diagonalization : PMSN neutrino mixing matrix :

  9. Currenteigenstate Masseigenstates (approximate) active neutrino mixing matrixfor neutrino oscillations Left-right neutrino mixing matrix

  10. Lesson : Two-generation case Without loss of generality, we can choose (1,1) elements are zeroby rotation of left- and right-handed fields.

  11. Features of this basis: In the limit b0, the matrix is rank 2. Easy to find a tiny active neutrino mass limit. Left-right mixing is characterized by

  12. Multiplying from both sides,

  13. After all, Diagonalization matrix of charged-lepton mass Diagonalization matrix of right-handed Majorana mass Note : precise experimental results require ~

  14. Three-generation case Without loss of generality, we can choose a basis: Features of this basis: In the limit b,d,e0, the 6x6 neutrino matrix is rank 3. Easy to find a tiny active neutrino mass limit. Left-right mixing is characterized by

  15. After all, Ex. LHC (same-sign muons) (T2K/MINOS/WCHOOZ/Daya Bay…)

  16. In old works in the literature, people works in the basis: is required for tiny neutrino mass. In our basis, The above condition is satisfied simply due to

  17. Experimental constraints (Atre-Han-Pascoli-Zhang)

  18. Colliders Tau and K, D meson decays Precision electroweak data Neutrino-less double beta decay Lepton flavor violation ~ (Fermi constant, lepton universality, invisible Z decay, …)

  19. Numerical Example (Unit in GeV)

  20. Key structure : small Rank reduced It can be realized by a flavor symmetry.

  21. Froggatt-Nielsen mechanism U(1): SU(2):

  22. Example: : B-L charged scalars which acquire VEV Dirac Yukawa :

  23. If both the Dirac and Majorana mass matrices are in the form : (x denotes non-zero entry.) the seesaw mass matrix is also in the form of

  24. Suppose that the mixings from the charged leptonare small, the Unitary matrix U is the MSN matrix. From the condition: we obtain …. Next page

  25. (Only the case of Normal hierarchy gives solutions in the setup.) Using the experimental data, we obtain 13 mixing as a prediction. (Cubic equation of 13 mixing for given CP phase).

  26. Current experimental best fit point :

  27. Same-sign di-lepton events at the LHC Resonant production (This is more important) Same-sign WW fusion

  28. Bare cross sections for same-sign di-muon (Atre-Han-Pascoli-Zhang) Datta-Guchait-Pilaftsis, Almeidia-Coutinho-Martins Simoes-do Vale, Panella-Cannoni-Carimalo-Srivastava, del Aguila-Aguilar-Saavedra,Chen-He-Tandean-Tsai, ….

  29. LHC sensitivity (Atre-Han-Pascoli-Zhang)

  30. Same-sign di-electron is strongly constraintedby double beta decay : Amplitude is proportional to . It can also controlled by a flavor symmetry. Same-sign di-electron can have a chance to be observed.

  31. Several special cases: 1 Double beta decay vanishes. 2 Two-lighter right-handed neutrino masses are degenerate. Double beta decay and μ e γvanish. 3 Two right-handed neutrino masses are degenerate. Lepton number(-like) symmetry remains. Degeneracy of Majorana neutrino Merit of TeV-scale resonant leptogenesis

  32. Summary We consider a convenient basis to describe the non-negligible left-right neutrino mixing. Tiny neutrino masses can be realized even ifthe left-right mixing is sizable. The neutrino mass structure can be controlled by a flavor symmetry. Same-sign di-electron events may be observed as well as di-muon events, satisfyingthe constraint of neutrino-less double beta decay.

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