The XXV International Symposium on Lattice Field Theory

We study cutoff effects at tree-level of perturbation theory for standard Wilson and Wilson twisted mass fermionic lattice actions with N f 2 flavour degenerate quarks. The discretization effects are investigated by computing the mass spectrum and decay amplitudes for different hadron inter-polating fields and the scaling behaviour towards the continuum limit is analyzed. It is shown that the Wilson and the mass average methods are equivalent and lead to O a improved 5-parity even lattice observables. We also demonstrate that automatic O a improvement works in case of Wilson twisted mass fermions at maximal twist and that this improvement is realized even if the condition of maximal twist is achieved only up to O a cutoff effects. We demonstrate that in the chiral limit standard Wilson fermions show scaling violations of O a2 while for maximally twisted mass fermions these violations are only of O a4 . For our analytical calculations, lattices with sizes L aN and periodic boundary conditions in the spatial directions have been chosen while infinite extension in the time direction, L4 ∞, is considered