Double beta decay and the extra-dimensional seesaw mechanism

Abstract

We study the model-building conditions under which an observable 0νββ-decay signal is predicted 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 S¹/Z₂ orbifold, where the Standard–Model fields are localized on a 3-brane. We show that sizeable 0νββ rates 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 MeV)^-1 characterizing the Fermi nuclear momentum. The resulting 5-dimensional models predict a sizeable effective Majorana-neutrino mass that could be several orders of magnitude larger than the light neutrino masses.