Flavor structure of the nucleon sea from lattice QCD

We present the first direct lattice calculation of the isovector sea-quark distributions in the nucleon within the framework of the large-momentum effective field theory proposed recently. We use N-f = 2 + 1 + 1 highly improved staggered quarks lattice gauge ensembles (generated by the MILC Collaboration) and clover valence fermions with pion mass 310 MeV. We establish the convergence of the result as the nucleon momentum increases within the uncertainty of the calculation. Although the lattice systematics are not yet fully under control, we obtain some qualitative features of the flavor structure of the nucleon sea: (d) over bar (x) > (u) over bar (x) leading to the violation of the Gottfried sum rule, Delta(u) over bar (x) > Delta(d) over bar (x) as indicated by the STAR data at large and small leptonic pseudorapidity.