Sea quark QED effects and twisted mass fermions

We show that maximally twisted mass fermions can be employed to regularize on the lattice the fully unquenched QCD+QED theory with vanishing q-term. We discuss how the critical mass of the up and down quarks can be conveniently determined beyond the electroquenched approximation by imposing that certain symmetries of continuum QCD+QED, which are broken byWilson terms, get restored in the continuum limit. A mixed action setup is outlined that allows to extend beyond the electroquenched approximation the computation (with only O(a2) artifacts) of the leading isospin breaking corrections to physical observables using the RM123 method and (pure QCD) ETMC gauge ensembles with Nf= 2+1+1 dynamical quark flavours.