An upper limit to the electric dipole moment of the neutron from lattice QCD

TL;DR

This paper establishes an upper limit on the neutron's electric dipole moment by analyzing lattice QCD simulations, linking topological susceptibility with parity and time-reversal symmetry breaking.

Contribution

It introduces a method to constrain the neutron EDM using lattice QCD simulations and volume scaling of topological susceptibility.

Findings

An upper limit on the neutron EDM is derived from lattice simulations.

Volume dependence of topological susceptibility signals symmetry breaking.

Results constrain possible new physics contributions to neutron EDM.

Abstract

A linear increase with the volume of the topological susceptibility can signal spontaneous breaking of parity and time inversion, due to a nonzero vacuum expectation value of the topological charge. Such a breaking would produce a nonzero electric dipole moment of the neutron, d_n. An upper limit to d_n is derived from numerical simulations at increasing volumes.