partner mechanism. Dimopoulos–Wilczek mechanism In an SO(10) theory, there is a potential solution to the doublet–triplet splitting problem known as the 'Dimopoulos–Wilczek' mechanism. In SO(10), the adjoint field, acquires a vacuum expectation value of the form . and give masses to the Higgs doublet and triplet, respectively, and are independent of each other, because is traceless for any values they may have. If , then the Higgs doublet remains massless. This is very similar to the way that doublet–triplet splitting is done in either higher-dimensional grand unified theories or string theory. 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. Higgs representations in Grand Unified Theories In SU(5): In SO(10): Proton decay 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. References 'Supersymmetry at Ordinary Energies. 1. Masses AND Conservation Laws.' Steven Weinberg. Published in Phys. Rev. D 26:287,1982. 'Proton Decay in Supersymmetric Models.' Savas Dimopoulos, Stuart A. Raby, Frank Wilczek. Published in Phys. Lett. B 112:133,1982. 'Incomplete Multiplets in Supersymmetric Unified Models.' Savas Dimopoulos, Frank Wilczek. External links (In this video from 12:00 to 18:00, Arkani-Hamed gives a brief discussion of the relation between the doublet–triplet splitting problem and the hierarchy problem.) Grand Unified Theory