The extraction of the axial coupling from finite volume systems: The long and short of it

Abstract

Due to a pion-pole contribution, the nucleon axial current matrix elements can be visualized in position space as becoming delocalized as the chiral limit is approached, with one-third of the current at distance of order the inverse pion mass. However, this delocalization effect will not cause calculations of the axial coupling in a finite system with standard boundary conditions (periodic for boson fields, antiperiodic for fermions) to have large finite volume effects. This is seen by calculating axial coupling using a nonstandard current with axial quantum numbers. The matrix elements of this new current lacks a pion pole and is not delocalized; however, its zero-momentum matrix element is identical to that of the standard axial current both for infinite and finite volumes.