# Beyond Neutrino Mass: Observable $n$-$\overline{n}$ Oscillations in UV Complete Seesaw Models

## TL;DR

This paper explores how neutron-antineutron oscillations, a rare baryon number violation process, can be naturally embedded in UV complete seesaw models within grand unified theories, linking observable phenomena to high-scale new physics.

## Contribution

It demonstrates that $n-ar{n}$ oscillations can originate from specific topologies in $SU(5)$ models with seesaw mechanisms, connecting low-energy experiments to grand unification.

## Key findings

- $n-ar{n}$ oscillations can be generated in $SU(5)$ frameworks.
- Upcoming experiments can probe colored states up to $10^{11}$ GeV.
- Link between baryon violation and fermion mass generation.

## Abstract

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 $\Delta B = 2$ baryon number violation, with particularly significant gains expected at the latter. The discovery of such a rare $\Delta B = 2$ 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 $\Delta B = 2$ processes can probe for a presence of the other colored states with masses up to $10^{11}\,\mathrm{GeV}$, 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.