Doublet–triplet splitting problem

In 'minimal' SU(5), the way one accomplishes doublet–triplet splitting is through a combination of interactions

that breaks SU(5) to the Standard Model gauge symmetry the Higgs doublets and triplets acquire a mass

After breaking to the SM the colour triplet can get super heavy, suppressing Proton decay, while the SM Higgs does not. Note that nevertheless the SM Higgs will have to pick up a mass in order to reproduce the electroweak theory correctly.

Note that although solving the DTS problem the MPM tends to render models Non-perturbative just above the GUT scale. This problem is addressed by the Double missing partner mechanism.

To arrange for the VEV to align along this direction (and still not mess up the other details of the model) often requires very contrived models, however.

Non-supersymmetric theories suffer from quartic radiative corrections to the mass squared of the electroweak Higgs boson (see hierarchy problem). In the presence of supersymmetry, the triplet Higgsino needs to be more massive than the GUT scale to prevent proton decay because it generates dimension 5 operators in MSSM; there it is not enough simply to require the triplet to have a GUT scale mass.