Intrinsic strangeness and charm of the nucleon using improved staggered fermions

Abstract

We calculate the intrinsic strangeness of the nucleon, $⟨N|\overline{s}s|N⟩\ensuremath{-}⟨0|\overline{s}s|0⟩$, using the MILC library of improved staggered gauge configurations using the Asqtad and HISQ actions. Additionally, we present a preliminary calculation of the intrinsic charm of the nucleon using the HISQ action with dynamical charm. The calculation is done with a method which incorporates features of both commonly used methods, the direct evaluation of the three-point function and the application of the Feynman-Hellman theorem. We present an improvement on this method that further reduces the statistical error, and check the result from this hybrid method against the other two methods and find that they are consistent. The values for $⟨N|\overline{s}s|N⟩$ and $⟨N|\overline{c}c|N⟩$ found here, together with perturbative results for heavy quarks, show that dark matter scattering through Higgs-like exchange receives roughly equal contributions from all heavy quark flavors.