N_f = 2+1+1 flavours of twisted mass quarks: cut-off effects at tree-level of perturbation theory

We present a calculation of cut-off effects at tree-level of perturbation theory for the K and D mesons using the twisted mass formulation of lattice QCD. The analytical calculations are performed in the time-momentum frame. The relative sizes of cut-off effects are compared for the pion, the kaon and the D meson masses. In addition, different realizations of maximal twist condition are considered and the corresponding cut-off effects are analyzed.