Sigma terms and strangeness content of the nucleon with $N_f=2+1+1$   twisted mass fermions
  We study the nucleon matrix elements of the quark scalar-density operator using maximally twisted mass fermions with dynamical light ($u$,$d$), strange and charm degrees of freedom. We demonstrate that in this setup the nucleon matrix elements of the light and strange quark densities can be obtained with good statistical accuracy, while for the charm quark counterpart only a bound can be provided. The present calculation which is performed at only one value of the lattice spacing and pion mass serves as a benchmark for a future more systematic computation of the scalar quark content of the nucleon. 
Simon Dinter, Vincent Drach, Roberto Frezzotti, Gregorio Herdoiza,   Karl Jansen, Giancarlo Rossi
hep-lat hep-ph