We study the model-building conditions under which a sizable $0\nu \beta \beta$-decay signal to the recently reported level of 0.4 eV is due to Kaluza-Klein singlet neutrinos in theories with large extra dimensions. Our analysis is based on 5-dimensional singlet-neutrino models compactified on an $S^1{/Z}_2$ orbifold, where the standard-model fields are localized on a 3-brane. We show that a successful interpretation of a positive signal within the above minimal 5-dimensional framework would require a non-vanishing shift of the 3-brane from the orbifold fixed points by an amount smaller than the typical scale $(100\mathrm{}\mathrm{MeV}{)}^{-1}$ characterizing the Fermi nuclear momentum. The resulting 5-dimensional models predict a sizable effective Majorana-neutrino mass that could be several orders of magnitude larger than the light neutrino masses. Most interestingly, the brane-shifted models with only one bulk sterile neutrino also predict novel trigonometric textures leading to mass scenarios with hierarchical active neutrinos and large ${\nu }_{\mu }-{\nu }_{\tau }$ and ${\nu }_e-{\nu }_{\mu }$ mixings that can fully explain the current atmospheric and solar neutrino data.

• Received 3 February 2003

DOI:https://doi.org/10.1103/PhysRevD.67.113001