Common origin of reactor and sterile neutrino mixing

Abstract

If the hints for light sterile neutrinos from short-baseline anomalies are to be taken seriously, global fits indicate active-sterile mixings of a magnitude comparable to the known reactor mixing. We therefore study the conditions under which the active-sterile and reactor mixings could have the same origin in an underlying flavour model. As a starting point, we use µ − τ symmetry in the active neutrino sector, which (for three neutrinos) yields a zero reactor neutrino angle and a maximal atmospheric one. We demonstrate that adding one sterile neutrino can change this setting, so that the active-sterile mixing and non-zero θ 13 can be generated simultaneously. From the phenomenological perspective, electron (anti)neutrino disappearance can be easily accommodated, while muon neutrino disappearance can vanish. Even the LSND results can be reconciled if the Majorana phases have very specific values. From the theory perspective, the setting requires the misalignment of some of the flavon vacuum expectation values, which may be achieved in an A 4 or D 4 flavour symmetry model using extra dimensions.

Nonzeroθ13with unbrokenμ−τsymmetry of the active neutrino mass matrix in the presence of a light sterile neutrino

“…Therefore, there is still room for the existence of an eV scale sterile neutrino within some specific BSM frameworks that can provide a consistent interpretation of experimental data. Here we intend to study the consequence of such 3 + 1 neutrino scenario on the µ − τ symmetry in a way first discussed by the authors of [26][27][28]. We in fact point out that, such a scenario of breaking µ − τ symmetry from the sterile neutrino sector can remain valid even if the present and future neutrino experiments conclusively rule out the 3 + 1 global fit data [35].…”

“…This was first proposed by the authors of [25] and was discussed in more details in [26][27][28] later on. This can have very interesting implications for neutrino model building in the presence of flavour symmetries.…”

“…Another interesting but much less explored idea to generate non-zero θ 13 is by allowing the mixing of three active neutrinos with a eV scale sterile neutrino [25][26][27][28]. For a review of light 2 For a recent review, please see [13].…”

“…As shown in [27,28], one can generate non-zero value for the reactor mixing angle θ 13 by introducing a breaking of µ−τ symmetry in the sterile sector that is, M µs = M τ s while keeping the 3×3 active neutrino block µ − τ symmetric. The authors of [28] derived approximate analytical expressions for the active neutrino mixing angles as a function of sterile neutrino parameters, by considering the effective 3 × 3 neutrino mass matrix after the decoupling of the sterile neutrino.…”

A White Paper on keV sterile neutrino Dark Matter

“…It is thus possible to see the actual effect of the A 4 symmetry: it leads to phenomenologically acceptable leptonic mixing. While the leading order terms generate a tri-bimaximal mixing matrix, which in particular features θ 13 ≡ 0 that is excluded as well as maximal θ 23 , the terms arising at next to leading order correct the mixing pattern such that a non-zero θ 13 , which can indeed arise from the sterile neutrino sector [810], and a deviation …”