Road map through the desert: unification with vector-like fermions

In light of null results from New Physics searches at the LHC, we look at unification of the gauge couplings as a model-building principle. As a first step, we consider extensions of the Standard Model with vector-like fermions. We present a comprehensive list of spectra that feature fermions in two distinct $SU(3)_C\times SU(2)_L\times U(1)_Y$ representations, in which precise gauge coupling unification is achieved. We derive upper and lower limits on vector-like masses from proton decay measurements, running of the strong gauge coupling, heavy stable charged particle searches, and electroweak precision tests. We demonstrate that due to a particular hierarchy among the mass parameters required by the unification condition, complementarity of various experimental strategies allows us to probe many of the successful scenarios up to at least 10 TeV.