LSND effect as a Chooz-restricted "sterile" perturbation of three-neutrino texture
Abstract
Description
Considering the hypothesis of mixing of three active neutrinos with, at least, one sterile neutrino, we report on a simple $4\times 4$ texture whose $ 3 \times 3 $ part arises from the popular bimaximal texture for three active neutrinos $ ν_e, ν_μ, ν_τ$, where $ c_{12} = 1/\sqrt{2} = s_{12}$, $ c_{23} = 1/\sqrt{2} = s_{23}$ and $ s_{13} = 0$. Such a $3\times 3 $ bimaximal texture is perturbed through a rotation in the 14 plane, where $ν_4 $ is the extra neutrino mass state induced by the sterile neutrino $ν_s $ which becomes responsible for the LSND effect. Then, with $m^2_1\simeq m^2_2$ we predict that $\sin^2 2θ_{\rm atm} = {1/2}(1+ c^2_{14}) \sim 0.99$ and $\sin^2 2θ_{\rm LSND} = {1/2}s^4_{14} \sim 4.5\times10^{-4}$, and in addition $ Δm^2_{\rm atm} = Δm^2_{32}$ and $ Δm^2_{\rm LSND} = |Δm^2_{41}|$, where $c^2_{14} = \sin^2 2θ_{\rm sol} \sim 0.97$ and $Δm^2_{21} = Δm^2_{\rm sol} \sim 10^{-7} {\rm eV}^2$ if {\it e.g.} the LOW solar solution is applied. In this four-neutrino texture with $m^2_1 \simeq m^2_2 $ the sum rule $\sin^2 2 θ_{\rm sol} + {1/2}\sin^2 2 θ_{\rm Chooz} + \sin^2 2 θ_{\rm LSND} = 1$ holds in the two-flavor approximation (for each of three cases), leaving room for the LSND effect, depending on the magnitude of Chooz effect that, not observed so far, leads (at present) to the upper bound $\sin^2 2θ_{\rm LSND}\stackrel{<}{\sim} 1.3\times10^{-3}$ and the lower bound $\sin^2 2θ_{\rm sol} \stackrel{>}{\sim} 0.95$. At the end a four-neutrino seesaw mechanism is sketched.
14 pages, latex, no figures
14 pages, latex, no figures