Nucleon matrix elements with $N_f=2+1+1$ maximally twisted fermions

We present the first lattice calculation of nucleon matrix elements using four dynamical flavors. We use the $N_f=2+1+1$ maximally twisted mass formulation. The renormalization is performed non-perturbatively in the RI$^\prime$-MOM scheme and results are given for the vector and axial vector operators with up to one-derivative. Our calculation of the average momentum of the unpolarized non-singlet parton distribution is presented and compared to our previous results obtained from the $N_f=2$ case.
Comment: 7 pages, 6 figures. Talk given at the XXVIII International Symposium on Lattice Field Theory, June 14-19, 2010, Villasimius, Sardinia Italy