GUT breaking on the lattice

We construct a supersymmetric grand unified model in the framework of a lat ticized extra dimension. The SU(5) symmetries on the lattice are broken by the vacuum expectation values of the link fields connecting adjacent SU(5) sites, leaving just the MSSM at low energies. Below the SU(5) breaking scal e, the theory gives rise to a similar spectrum as in orbifold breaking of S U(5) symmetry in 5 dimensions, and shares many features with the latter sce nario. We discuss gauge coupling unification and proton decay emphasizing t he differences with respect to the usual grand unified theories. Our model may be viewed as an effective four-dimensional description of the orbifold symmetry breaking in higher dimensions. (C) 2001 Published by Elsevier Scie nce B.V.