Neutron-antineutron oscillations on the lattice

TL;DR

This paper discusses the calculation of neutron-antineutron oscillation matrix elements using lattice QCD, which is crucial for understanding baryon number violation and constraining grand unified theories.

Contribution

It presents the formalism and preliminary lattice QCD results for neutron-antineutron transition matrix elements, advancing non-perturbative predictions for BSM physics.

Findings

Preliminary results from $32^3\times256$ lattices with a 390 MeV pion mass.

Formalism for calculating six-quark matrix elements on the lattice.

Insights into baryon number violation relevant for GUT constraints.

Abstract

One possible low energy process due to beyond the Standard Model (BSM) physics is the neutron-antineutron transition, where baryon number changes by two units. In addition to providing a source of baryon number violation in the early universe, interactions of this kind are natural in grand unified theories (GUTs) with Majorana neutrinos that violate lepton number. Bounds on these oscillations can greatly restrict a variety of GUTs, while a non-zero signal would be a "smoking gun" for new physics; however, to make a reliable prediction, the six-quark nucleon-antinucleon matrix elements must first be calculated non-perturbatively via lattice QCD. We review the current understanding of this quantity, describe the lattice formalism, and present preliminary results from $32^3\times256$ clover-Wilson lattices with a pion mass of 390 MeV.