Higher dimensional models of light Majorana neutrinos confronted by data

We discuss experimental and observational constraints on certain models of higher dimensional light Majorana neutrinos. Models with flavor blind brane-bulk couplings plus three or four flavor diagonal light Majorana neutrinos on the brane, with subsequent mixing induced solely by the Kaluza-Klein tower of states, are found to be excluded by data on the oscillations of solar, atmospheric and reactor neutrinos, taken together with the cosmological upper bound on the sum of neutrino masses. Extra dimensions, if relevant to neutrino mixing, need to discriminate between neutrino flavors.

Figure 1

Allowed regions in the $m_1$ and $m_3$ plane for (a) the normal ordering and (b) the inverted ordering of neutrino masses. Choices of parameters are described in the text.

Figure 2

Time-averaged oscillation probabilities $\overline{P_{\mathrm{a}\mathrm{t}\mathrm{m}}}$ (stars) and $\overline{P_{\mathrm{s}\mathrm{o}\mathrm{l}}}$ (triangles) for the inverted ordering of neutrino masses as a function of $m_3$. Only those points are considered here which satisfy for $\overline{P_{\mathrm{a}\mathrm{t}\mathrm{m}}}$ the $\mathrm{\text{Solar}}+\mathrm{C}\mathrm{H}\mathrm{O}\mathrm{O}\mathrm{Z}$ constraints and for $\overline{P_{\mathrm{s}\mathrm{o}\mathrm{l}}}$ the $\mathrm{\text{Atmospheric}}+\mathrm{C}\mathrm{H}\mathrm{O}\mathrm{O}\mathrm{Z}$ constraints.