Strange quark contributions to nucleon mass and spin from lattice QCD

Abstract

Contributions of strange quarks to the mass and spin of the nucleon, characterized by the observables ${f}_{{T}_{s}}$ and $\ensuremath{\Delta}s$, 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, ${m}_{\ensuremath{\pi}}=495$, 356, and 293 MeV, renormalized, and chirally extrapolated to the physical pion mass. The value extracted for $\ensuremath{\Delta}s$ at the physical pion mass in the $\overline{\mathrm{MS}}$ scheme at a scale of 2 GeV is $\ensuremath{\Delta}s=\ensuremath{-}0.031(17)$, whereas the strange quark contribution to the nucleon mass amounts to ${f}_{{T}_{s}}=0.046(11)$. In the employed mixed-action scheme, the nucleon valence quarks as well as the strange quarks entering the nucleon matrix elements that determine ${f}_{{T}_{s}}$ and $\ensuremath{\Delta}s$ 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 ${f}_{{T}_{s}}$.