The Potential Fate of Local Model Building

We analyse local models at the point of E_8 in F-theory GUTs and identify exactly two models with potentially realistic properties concerning proton stability and a suitable pattern of quark and lepton masses. To this end we identify a matter parity at the local point. A globally consistent ultraviolet completion turns out to be problematic for both models. It is impossible to embed the models in a semilocal scheme via the spectral cover approach. This seems to severely limit the predictive power of local model building and to indicate that the full string theory might give us valuable hints for particle physics model building.