Strange quark contributions to nucleon mass and spin from lattice QCD
Contributions of strange quark degrees of freedom to the mass and spin of the nucleon, characterized by the observables f_Ts and Delta s, respectively, are investigated in a 2+1-flavor mixed-action lattice scheme. Numerical results are obtained at three pion masses, m_pi = 495 MeV, 356 MeV, and 293 MeV, and chirally extrapolated to the physical pion mass. In the case of Delta s, in particular, these are the first renormalized, chirally extrapolated lattice QCD results obtained using fully dynamical strange quark degrees of freedom. 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.