NATURALLY LIGHT HIGGS DOUBLET IN THE SPINOR REPRESENTATION OF SUSY SO(10)

Within the supersymmetric SO(10) GUT we explore the possibility of the light Higgs doublet being a member of the 16-dimensional spinorial re presentation. This fact is ultimately related with the assumption that the light matter (at least partially) resides in some of the tensor r epresentations as well. Several interesting features emerge. First, pr ovided that the same 16-plet is responsible for the breaking SO(10) -- > SU(5), the heaviness of the top can automatically follow from the fi eld content at M(GUT), without need of any flavour symmetries. Secondl y, the doublet-triplet splitting problem receives a new natural soluti on. In addition, a dimension = 5 (Higgsino mediated) proton decay can be naturally suppressed. We construct explicit SO(10) models with the above properties, with most general superpotentials under the symmetri es.