On neutrino masses and mixings from extra dimensions

In the framework of a Kaluza-Klein type theory with the Standard Model fields localized on a 4-dimensional section while gravity propagates in a full 4 + delta-dimensional space-time, we examine a mechanism of naturally small neutrino mass generation through couplings of the Standard Model singlet fermion(s) living also in the full space-time. A numerical study is carried out on the charged current universality constraint from the ratio of pion decay partial widths. The bounds obtained on the fundamental mass scale could be stringent. (C) 1999 Published by Elsevier Science B.V. All rights reserved.