Strange Quark Condensate in the Nucleon in 2+1 Flavor QCD

We calculate the strange quark content of the nucleon, << N vertical bar ss vertical bar N >>, which is important for interpreting the results of some dark matter detection experiments. The method is to evaluate quark-line disconnected correlations on the MILC lattice ensembles, which include the effects of dynamical light and strange quarks. After continuum and chiral extrapolations, the result is << N vertical bar ss vertical bar N >>=0.69(7)(stat)(9)(syst), in the modified minimal subtraction scheme (2 GeV) regularization, or for the renormalization scheme invariant form, m(s)M(N)partial derivative m(s)=59(6)(8) MeV.