Neutrino Mass Induced $n$-$\overline{n}$ Oscillation

TL;DR

This paper showcases a fundamental link between Majorana neutrino mass generation and neutron–antineutron oscillation within SU(5) grand unification. By arguing that $| abla L|=2$ Majorana masses necessarily break $U(1)_{B-L}$ by two units, it demonstrates that this breaking induces $| abla B|=2$ processes via a $d=9$ operator, connecting neutrino masses to $n$–$ar n$ oscillations. The authors classify the simplest renormalizable extensions of the Georgi–Glashow model that produce viable Majorana masses (covering Type I/II/III seesaws and one-/two-loop radiative models) and map each scenario to specific $n$–$ar n$ topologies (A, AI, AII, B, C) with dominant mediators. They conclude that these extensions predict an additional baryon-number-violating channel beyond proton decay and highlight complementary probes such as $0 uetaeta$, lepton-flavor violation, and di-nucleon decays, motivating targeted experimental searches and further renormalizable model studies.

Abstract

The Georgi-Glashow model is the simplest possible attempt at grand unification. However, due to its particle content, it preserves a global $U(1)_{B-L}$ symmetry, where $B$ and $L$ are baryon and lepton numbers, respectively. It thus leaves neutrinos massless just as in the Standard Model. Extensions of the Georgi-Glashow model that break lepton number by two units, i.e., scenarios with $|ΔL|=2$ operator(s), naturally generate potentially viable Majorana neutrino masses. Consequently, $B-L$ breaking via the same dynamics that yields $|ΔL| = 2$ interactions unavoidably induces $|ΔB| = 2$ transitions, leading to intriguing processes such as neutron-antineutron ($n$-$\overline{n}$) oscillation. We demonstrate this intrinsic connection between neutrino mass generation and $n$-$\overline{n}$ oscillation within tree-level seesaw mechanisms of the Type I, II, and III varieties, as well as in the one-loop and two-loop radiative neutrino mass models. Our study exhausts the simplest possible extensions of the Georgi-Glashow model that yield realistic neutrino masses and mixing parameters and, in the process, induce $n$-$\overline{n}$ oscillation.

Figures (6)

• Figure 1: A schematic of an interplay between quark-lepton unification and neutrino mass generation with respect to the proton decay, $n$--$\overline{n}$ oscillation, and neutrinoless double beta decay ($0\nu\beta\beta$) processes.
• Figure 2: Type I/III seesaws (upper panel) and the associated topology, i.e., TOPOLOGY B, behind $n$--$\overline n$ oscillation (lower panel).
• Figure 3: Type II seesaw mechanism (upper panel) and the associated topology, i.e., TOPOLOGY A, behind $n$--$\overline n$ oscillation (lower panel).
• Figure 4: Babu–Nandi–Tavartkiladze (BNT) mechanism (upper panel) and associated $n$--$\overline n$ oscillation diagram (lower panel).
• Figure 5: Zee mechanism (upper panel) and the associated topology, i.e., TOPOLOGY AI, behind $n$--$\overline n$ oscillation (lower panel).