Next-generation experiments, such as the Deep Underground Neutrino Experiment and the European Spallation Source, are set to improve sensitivity to neutron-antineutron oscillation, a direct probe of ∆B = 2 baryon number violation, with particularly significant gains expected at the latter. The discovery of such a rare ∆B = 2 process would indicate physics beyond the Standard Model and could point to specific unified theories that allow observable \( n-\overline{n} \) transitions. We accordingly examine \( n-\overline{n} \) oscillations within a unified framework that accounts for charged fermion masses and generates viable neutrino masses via the seesaw mechanism. More specifically, we show that \( n-\overline{n} \) oscillations can arise from two specific topologies within two distinct SU(5) scenarios. One topology requires a presence of two color-sextet scalars in the Type II seesaw framework, whereas the other involves a scalar sextet and a color-octet fermion in the Type III seesaw framework. While the former topology can be realized in the SO(10)/Pati-Salam frameworks, the latter finds a natural embedding in SU(5), which constitutes one of the key novelties of our work. Remarkably enough, the same dynamics responsible for fermion masses also induces baryon number violation, thus linking \( n-\overline{n} \) oscillations to the flavor structure of the theory. We show that, given a TeV-scale mass for one of the colored states, upcoming searches for such ∆B = 2 processes can probe for a presence of the other colored states with masses up to 1011 GeV, well beyond the reach of colliders. This positions \( n-\overline{n} \) oscillations as a rare low-energy portal to grand unification and ultra-heavy new physics.
