Flipping SU(5) towards five-dimensional unification
It is shown that embedding of flipped $\mathrm{SU}(5)$ in a five-dimensional $\mathrm{SO}(10)$ enables exact unification of the gauge coupling constants. The demand for unification uniquely determines both the compactification scale and the cutoff scale. These are found to be ${M}_{C}\ensuremath{\approx}5.5\ifmmode\times\else\texttimes\fi{}{10}^{14}\mathrm{GeV},$ and ${M}_{*}\ensuremath{\approx}1.0\ifmmode\times\else\texttimes\fi{}{10}^{17}\mathrm{GeV},$ respectively. The theory explains the absence of $d=5$ proton-decay operators through the implementation of the missing partner mechanism. On the other hand, the presence of $d=6$ proton-decay operators points towards the bulk localization of the first and second families of matter fields.