Common origin ofμ−τandCPbreaking in the neutrino seesaw, baryon asymmetry, and hidden flavor symmetry

Abstract

We conjecture that all CP violations (both Dirac and Majorana types) arise from a common origin in neutrino seesaw. With this conceptually attractive and simple conjecture, we deduce that µ−τ breaking shares the common origin with all CP violations. We study the common origin of µ − τ and CP breaking in the Dirac mass matrix of seesaw Lagrangian (with right-handed neutrinos being µ−τ blind), which uniquely leads to inverted mass-ordering of light neutrinos. We then predict a very different correlation between the two small µ−τ breaking observables θ 13 − 0• and θ 23 − 45• , which can saturate the present experimental upper limit on θ 13 . This will be tested against our previous normal mass-ordering scheme by the on-going oscillation experiments. We also analyze the correlations of θ 13 with Jarlskog invariant and neutrinoless ββ-decay observable. From the common origin of CP and µ − τ breaking in the neutrino seesaw, we establish a direct link between the low energy CP violations and the cosmological CP violation for baryon asymmetry. With these we further predict a lower bound on θ13 , supporting the on-going probes of θ13 at Daya Bay, Double Chooz and RENO experiments. Finally, we analyze the general model-independent Z2 ⊗ Z2 symmetry structure of the light neutrino sector, and map it into the seesaw sector, where one of the Z2's corresponds to the µ−τ symmetry Z µτ 2 and another the hidden symmetry Z s 2 (revealed in our previous work) which dictates the solar mixing angle θ12 . We derive the physical consequences of this Z s 2 and its possible partial violation in the presence of µ−τ breaking (without or with neutrino seesaw), regarding the θ12 determination and the correlation between µ−τ breaking observables.[ arXiv: 1104.2654 ]

Double seesaw mechanism and lepton mixing

“…Due to the double seesaw mechanism, the mass scale m ν of the light neutrinos is determined by Our flavour symmetries are arranged in such a way that, in an appropriate weak basis, the contribution to the lepton mixing matrix U from the charged-lepton sector is given by U ω of eq. (1.3), whereas the neutrino sector contributes a matrix V constrained by either one or two 2 symmetries [10][11][12][13][14][15][16][17][18][19][20][21][22]. The matrix V is exclusively determined by the Majorana mass matrix M of the N jR .…”

“…Then, by slight variations of the symmetries of the model and of the soft breaking, we show in section 3 how to realize other mixing schemes like the ones in refs. [10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Our conclusions are presented in section 4.…”

“…[10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Our framework relies on the double seesaw mechanism and on a soft flavour symmetry breaking in the Majorana mass matrix of right-handed neutrino singlets; it involves neither of the technical complications mentioned in the previous paragraph.…”

“…On the other hand, many authors [10][11][12][13][14][15][16][17][18][19][20][21][22] have recently pursued an approach in which U is either partially or completely determined by distinct symmetries in the chargedlepton mass matrix M ℓ and in the light-neutrino Majorana mass matrix M ν . Those distinct symmetries are conceived as remnants of the full flavour symmetry group of the Lagrangian.…”

Minimal modifications to the Tri-Bimaximal neutrino mixing

“…Eq. (2.1) can also be understood in terms of the µ − τ symmetry [36] and its breaking [37][38][39][40][41][42][43][44]. As pointed out in ref.…”