Restless pions: orbifold boundary conditions and noise suppression in lattice QCD

TL;DR

This paper introduces a novel boundary condition in lattice QCD called 'restless pions' that removes zero momentum pion modes, enhancing the signal-to-noise ratio for baryon studies and aiding nuclear force investigations.

Contribution

It proposes a parity orbifold boundary condition that raises the minimum pion energy, improving long-time baryon signal quality without changing the ground state.

Findings

Elimination of zero momentum pion modes increases minimum pion energy.

Improved signal-to-noise ratio for baryon correlation functions.

Potential benefits for studying nuclear forces in lattice QCD.

Abstract

The study of one or more baryons in lattice QCD is severely hindered by the exponential decay in time of the signal-to-noise ratio. The rate at which the signal-to-noise decreases is a function of the the pion mass. More precisely, it depends on the minimum allowed pion energy in the box, which, for periodic boundary conditions, is equal to its mass. We propose a set of boundary conditions, given by a "parity orbifold'' construction, which eliminates the zero momentum pion modes, raising the minimum pion energy without altering the QCD ground state, and thereby improving the signal-to-noise ratio of (multi)-baryon correlation functions at long Euclidean times. We discuss variations of these "restless pions" boundary conditions and focus on their impact on the study of nuclear forces.