Strange quark contributions to nucleon mass and spin from lattice QCD

Contributions of strange quarks to the mass and spin of the nucleon, characterized by the observables f_Tₛ and Δs, 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_π=495, 356, and 293 MeV, renormalized, and chirally extrapolated to the physical pion mass. The value extracted for Δs at the physical pion mass in the MS̄ scheme at a scale of 2 GeV is Δs=-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 that determine f_Tₛ and Δs 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.