Disconnected quark loop contributions to nucleon observables in lattice QCD

One additional figure, typos corrected, version to appear in Phys. Rev. D. 14 pages and 14 figures. arXiv admin note: text overlap with arXiv:1309.2256We perform a high statistics calculation of disconnected fermion loops on Graphics Processing Units for a range of nucleon matrix elements extracted using lattice QCD. The isoscalar electromagnetic and axial vector form factors, the sigma-terms and the momentum fraction and helicity are among the quantities we evaluate. We compare the disconnected contributions to the connected ones and give the physical implications on nucleon observables that probe its structure