Results on the electromagnetic form factors of the nucleon using twisted mass fermion configurations are presented. These include a gauge field ensemble simulated with two degenerate light quarks yielding a pion mass of around 130 MeV, as well as two
ensembles that include strange and charm quarks in the sea yielding pion masses of 210 MeV and 373 MeV. Details of the methods used and systematic errors are discussed, such as noise reduction techniques and the effect of excited states contamination.
We present a calculation of the ratio of the charm quark mass to the strange quark mass. Using the Brillouin improved Wilson action, we are able to calculate this ratio in a single framework, using a relativistic fermionic action throughout. The calc
ulation is carried out on selected ensembles of two flavor clover improved lattices produced by the QCDSF collaboration, allowing an extrapolation to the continuum, to infinite volume and to the physical pion mass.
We develop the formalism for the evaluation of density-density correlators in lattice QCD that includes techniques for the computation of the all-to-all propagators involved. A novel technique in this context is the implementation of the one-end tric
k in the meson sector. Density-density correlators provide a gauge invariant definition for the hadron wave function and yield information on hadron deformation. We evaluate density-density correlators using two degenerate flavors of dynamical Wilson fermions for the pion, the rho-meson, the nucleon and the $Delta$. Using the one-end trick we obtain results that clearly show deformation of the rho-meson.
Hadron wave functions and form factors can be extracted using four-point correlators. Stochastic techniques are used to estimate the all to all propagators, which are required for the exact calculation of four-point functions. We apply the so called
one-end trick to evaluate meson four-point functions. We demonstrate the effectiveness of the technique in the case of the pion and the $rho$-meson where we extract their charge distribution, as well as the form factors.
