Triplet-extended scalar sector and the naturalness problem

Abstract

We consider the extension of the Standard Model by a complex scalar triplet field, which occurs naturally in several models of leptogenesis and see-saw mechanism for neutrino mass generation, in the context of ameliorating the fine-tuning problem of the fundamental scalars through the Veltman Condition, i.e. by demanding the sum of the quadratically divergent corrections to vanish (or be at a reasonable level) by virtue of some possible symmetry of the underlying theory. We show that it is possible to cancel all the scalar one-loop quadratic divergences and hence obtain a viable solution for the fine-tuning problem, while satisfying the electroweak precision observables, including the $\rho$ parameter, and successfully generating the neutrino masses. The stability of the scalar potential puts important constraints on the model.

Comments: v2: 11 pages, including 5 eps figures. A new section on scalar spectrum added. A typo corrected. Lots of references added. All results of the previous version unchanged. Version to be published in Phys. Rev. D