Arkani-Hamed and Schmaltz have shown that proton stability need not originate from symmetries in a high energy theory. Instead the proton decay rate is suppressed if quarks and leptons are spatially separated in a compact extra dimension. This separation may be achieved by coupling five-dimensional fermions to a bulk scalar field with a nontrivial vacuum profile and requires relationships between the associated quark and lepton Yukawa couplings. We hypothesize that these relationships are the manifestation of an underlying symmetry. We further show that the Arkani-Hamed and Schmaltz proposal may suggest that proton stability is the result of an underlying symmetry, though not necessarily the traditional baryon number symmetry.

• Received 23 June 2006

DOI:https://doi.org/10.1103/PhysRevD.74.127701