Proton stability in TeV-scale GUTs

We discuss the proton decay problem in theories with low gravity and/or GUT scales. We pointed out that the gravity induced proton decay can be indeed suppressed up to a desired level, while the GUT origin of the proton insta bility is rather problematic. To solve this problem we suggest the GUT mode l where the proton is stable in all orders of perturbation theory. This can be simply achieved by the replication of quark-lepton families with ordina ry quarks and leptons residing in different GUT representations and by an a ppropriate dimensional reduction. The model predicts extra mirror states wh ich along with the GUT particles and the excitations of extra dimensions co uld be observable at high-energy colliders providing the unification scale is in the TeV range. (C) 2001 Elsevier Science B.V. All rights reserved.