A lattice study of the strangeness content of the nucleon

TL;DR

This study uses lattice QCD simulations to quantify the strangeness and light quark contributions to the nucleon’s spin and mass, providing new insights into nucleon structure.

Contribution

It presents the first lattice QCD calculation of the strangeness content of the nucleon, including sigma-terms and spin contributions, with non-perturbative renormalization.

Findings

Sigma_{piN} = 38(12) MeV at physical quark masses

Strangeness fraction f_{Ts} = 0.012(14)

Strangeness contribution to nucleon spin Delta s = -0.020(10)

Abstract

We determine the quark contributions to the nucleon spin Delta s, Delta u and Delta d as well as their contributions to the nucleon mass, the sigma-terms. This is done by computing both, the quark line connected and disconnected contributions to the respective matrix elements, using the non-perturbatively improved Sheikholeslami-Wohlert Wilson Fermionic action. We simulate n_F=2 mass degenerate sea quarks with a pion mass of about 285 MeV and a lattice spacing a = 0.073 fm. The renormalization of the matrix elements involves mixing between contributions from different quark flavours. The pion-nucleon sigma-term is extrapolated to physical quark masses exploiting the sea quark mass dependence of the nucleon mass. We obtain the renormalized value sigma_{piN}=38(12) MeV at the physical point and the strangeness fraction f_{Ts}=sigma_s/m_N=0.012(14)(+10-3) at our larger than physical sea quark mass. For the strangeness contribution to the nucleon spin we obtain in the MSbar scheme at the renormalization scale of 2.71 GeV Delta s = -0.020(10)(2).