Orthogonal U(1) symmetries, proton stability, and extra dimensions - art. no. 075012

In models with a low quantum gravity scale, one might expect that all opera tors consistent with gauge symmetries are present in the low-energy effecti ve theory. If this is the case, some mechanism must be present to adequatel y suppress operators that violate baryon number. Here we explore the possib ility that the desired suppression is a consequence of an additional, spont aneously broken, nonanomalous U(1) symmetry that is orthogonal to hyperchar ge. We show that successful models can be constructed in which the addition al particle content necessary to cancel anomalies is minimal and compatible with the constraints from precision electroweak measurements and gauge uni fication. If unification is sacrificed, and only the new U(1) and its assoc iated Higgs fields live in the bulk, it is possible that the gauge field ze ro mode and first few Kaluza-Klein excitations lie within the kinematic rea ch of the Fermilab Tevatron. For gauge couplings not much smaller than that of hypercharge, we show that these highly leptophobic states could evade d etection at run I, but be discovered at run II. Our scenario presents an al ternative to the "cartographic" solution to baryon number violation in whic h leptons and quarks are separated in an extra dimension.