Strangeness Contribution to the Proton Spin from Lattice QCD

We compute the strangeness and light-quark contributions Delta s, Delta u, and Delta d to the proton spin in n(f) = 2 lattice QCD at a pion mass of about 285 MeV and at a lattice spacing a approximate to 0.073 fm, using the nonperturbatively improved Sheikholeslami-Wohlert Wilson action. We carry out the renormalization of these matrix elements, which involves mixing between contributions from different quark flavors. Our main result is the small negative value Delta s((MS) over bar)(root 7.4 GeV) = -0.020(10)(4) of the strangeness contribution to the nucleon spin. The second error is an estimate of the uncertainty, due to the missing extrapolation to the physical point.