  Wilson Fermions with untwisted and twisted mass are widely used in lattice
simulations. Therefore one important question is whether the twist angle and
the lattice spacing affect the phase diagram. We briefly report on the study of
the phase diagram of QCD in the parameter space of the degenerate quark masses,
isospin chemical potential, lattice spacing, and twist angle by employing
chiral perturbation theory. Moreover we calculate the pion masses and their
dependence on these four parameters.
