Controlling Excited-State Contributions with Distillation in Lattice QCD Calculations of Nucleon Isovector Charges $g_S^{u-d}$, $g_A^{u-d}$, $g_T^{u-d}$

TL;DR

This paper demonstrates that distillation smearing combined with the variational method improves the precision and control of excited-state contributions in lattice QCD calculations of nucleon isovector charges, reducing statistical uncertainties.

Contribution

The study introduces the application of distillation smearing with the variational method to enhance nucleon charge calculations in lattice QCD, showing improved accuracy and efficiency.

Findings

Distillation reduces statistical uncertainties compared to other smearing methods.

Distillation provides better control over excited-state contamination.

The variational method offers additional benefits without extra computational cost.

Abstract

We investigate the application of the distillation smearing approach, and the use of the variational method with an extended basis of operators facilitated by this approach, on the calculation of the nucleon isovector charges $g_S^{u-d}$, $g_A^{u-d}$, and $g_T^{u-d}$. We find that the better sampling of the lattice enabled through the use of distillation yields a substantial reduction in the statistical uncertainty in comparison with the use of alternative smearing methods, and furthermore, appears to offer better control over the contribution of excited-states compared to use of a single, local interpolating operator. The additional benefit arising through the use of the variational method in the distillation approach is less dramatic, but nevertheless significant given that it requires no additional Dirac inversions.