  We consider explicit unified models based on the flipped ${SU(5)\times U(1)}$
and $SU(6)\times SU(2)$ gauge groups in which gauge mediated proton decay
operators are suppressed at leading order due to the special placement of
matter fields in unified multiplets. We discuss both the theoretical structure
and phenomenological implications of these models. For the latter, we examine
the viability of the physical spectrum in each scenario and focus on the
possible presence of other operators that could also contribute significantly
to the proton decay rate.

High Energy Physics - Phenomenology