Strange quark contributions to nucleon mass and spin from lattice QCD

TL;DR

This paper uses lattice QCD with a mixed-action scheme to quantify strange quark contributions to the nucleon’s mass and spin, providing new numerical estimates at physical pion mass.

Contribution

It presents the first lattice QCD calculation of strange quark contributions to nucleon mass and spin using a 2+1-flavor mixed-action scheme with domain wall fermions.

Findings

Delta s = -0.031(17) at physical pion mass

f_Ts = 0.046(11) at physical pion mass

Results are obtained with mild renormalization behavior

Abstract

Contributions of strange quarks to the mass and spin of the nucleon, characterized by the observables f_Ts and Delta s, respectively, are investigated within lattice QCD. The calculation employs a 2+1-flavor mixed-action lattice scheme, thus treating the strange quark degrees of freedom in dynamical fashion. Numerical results are obtained at three pion masses, m_pi = 495 MeV, 356 MeV, and 293 MeV, renormalized, and chirally extrapolated to the physical pion mass. The value extracted for Delta s at the physical pion mass in the MSbar scheme at a scale of 2 GeV is Delta s = -0.031(17), whereas the strange quark contribution to the nucleon mass amounts to f_Ts =0.046(11). In the employed mixed-action scheme, the nucleon valence quarks as well as the strange quarks entering the nucleon matrix elements which determine f_Ts and Delta s are realized as domain wall fermions, propagators of which are evaluated in MILC 2+1-flavor dynamical asqtad quark ensembles. The use of domain wall fermions leads to mild renormalization behavior which proves especially advantageous in the extraction of f_Ts.