Presentation on theme: "TeV-scale seesaw with non-negligible left-right neutrino mixings Yukihiro Mimura (National Taiwan University) Based on arXiv:1110.2252 [hep-ph] Collaboration."— Presentation transcript:
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) 1 Seminar at Academia Sinica (2012.1.13, Friday)
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: 1.Find a convenient flavor basis to describe the non-negligible left-right neutrino mixing. 2.Consider a flavor symmetry to obtain a sizable left-right neutrino mixing. 3.Experimental implication
7 What we see in this talk: 1.Introduction (Done) 2.Convenient basis to describe the left-right neutrino mixing 3.Experimental constraints 4.Flavor symmetry 5.Experimental implications 6.Summary
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: In the limit b,d,e 0, the 6x6 neutrino matrix is rank 3. Features of this basis: Easy to find a tiny active neutrino mass limit. Left-right mixing is characterized by
15 After all, Ex. (T2K/MINOS/WCHOOZ/Daya Bay…) LHC (same-sign muons)
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
30 Same-sign di-electron is strongly constrainted by 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: Two-lighter right-handed neutrino masses are degenerate. Double beta decay vanishes. Double beta decay and μ e γ vanish. Two right-handed neutrino masses are degenerate. Lepton number(-like) symmetry remains. Degeneracy of Majorana neutrino Merit of TeV-scale resonant leptogenesis 1 2 3
32 Summary 1.We consider a convenient basis to describe the non-negligible left-right neutrino mixing. 2.Tiny neutrino masses can be realized even if the left-right mixing is sizable. 3.The neutrino mass structure can be controlled by a flavor symmetry. 4.Same-sign di-electron events may be observed as well as di-muon events, satisfying the constraint of neutrino-less double beta decay.