Nucleon isovector scalar charge from overlap fermions

TL;DR

This study computes the nucleon isovector scalar charge using lattice QCD with overlap fermions across multiple ensembles, extrapolating to physical conditions to provide a precise value relevant for understanding nucleon structure.

Contribution

It presents a novel lattice QCD calculation of the nucleon isovector scalar charge using overlap fermions with comprehensive control over systematic uncertainties.

Findings

Final result: $g_{S}^{u-d}= 0.94 (10)_{stat}(8)_{sys}$ at 2 GeV

Controlled extrapolation to physical pion mass, continuum, and infinite volume limits

Careful analysis of excited-states contamination with multi-state fits

Abstract

We calculate the nucleon isovector scalar charge in lattice QCD using overlap fermions on five ensembles of gauge configurations generated by the RBC/UKQCD collaboration using the domain-wall quark action with $2+1$ dynamical flavors. The five ensembles cover five pion masses, $m_\pi \approx$ 139, 171, 302, 337 and 371 MeV, and four lattice spacings, $a \approx $ 0.06, 0.08, 0.11 and 0.14 fm. Three to six valence quark masses are computed on each ensemble to investigate the pion mass dependence. The extrapolation to the physical pion mass, continuum and infinite volume limits is obtained by a global fit of all data to a formula originated from partially quenched chiral perturbation theory. The excited-states contamination is carefully analyzed with 3--5 sink-source separations and multi-state fits. Our final result, in the $\overline{\text{MS}}$ scheme at 2 GeV, is $g_{S}^{u-d}= 0.94 (10)_{stat}(8)_{sys}$, where the first error is the statistical error and the second is the systematic error.