2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/104533It is shown that in SO(10) and SU(5) models having a $U(1)_R$ symmetry, the requirement of breaking the unified group to the Standard Model leads to flat directions in the scalar potential. These can lead to a ``cosmological modulus problem". This is relevant to grand unified models of inflation, where $U(1)_R$ symmetries are often used to insure the flatness of the inflaton potential. A way that the modulus problem might be avoided is discussed.1+17 pages, 1 eps figureHigh Energy Physics - Phenomenologytext