Nucleon Charges, Form-factors and Neutron EDM

TL;DR

This paper updates lattice QCD calculations of nucleon charges with improved error analysis, using multiple ensembles and methods, and explores implications for neutron EDM and split SUSY models.

Contribution

It provides the most recent, precise lattice QCD results for nucleon charges and their systematic error control, and analyzes their impact on neutron EDM constraints in new physics models.

Findings

Calculated nucleon charges with reduced uncertainties.

Performed continuum and physical pion mass extrapolations.

Analyzed implications for neutron EDM and split SUSY.

Abstract

We present an update of our analysis of statistical and systematic errors in the calculation of iso-vector scalar, axial and tensor charges of the nucleon. The calculations are done using $N_f=2+1+1$ flavor HISQ ensembles generated by the MILC Collaboration at three values of the lattice spacing ($a=0.12,\ 0.09,$ and $0.06$ fm) and three values of the quark mass ($M_\pi \approx 310,\ 220$ and $130$ MeV); and clover fermions for calculating the correlation functions, i.e., we use a clover-on-HISQ lattice formulation. The all-mode-averaging method allows us to increase the statistics by a factor of eight for the same computational cost leading to a better understanding of and control over excited state contamination. Our current results, after extrapolation to the continuum limit and physical pion mass are $g_A^{u-d} = 1.21(3)$, $g_T^{u-d} = 1.005(59)$ and $g_S^{u-d} = 0.95(12) $. Further checks of control over all systematic errors, especially in $g_A^{u-d}$, are still being performed. Using results for the flavor-diagonal charges, $g_T^{u} $, $g_T^{d} $ and $g_T^{s}$, we analyze contributions of the quark electric dipole moment to the neutron EDM and the consequences for split SUSY model.