Improving the tunings of the MSSM by adding triplets and singlet

Abstract

We study an extension of the MSSM which includes both new SU(2) triplets with hypercharge $\pm 1$ and a SM gauge singlet (a la NMSSM) which are coupled to each other. We are motivated by the little hierarchy problem, as well as by the $\hat{I}¼$ problem of the MSSM. We show that the NMSSM and the triplet-extended MSSM can successfully solve problems of one another: while triplets are responsible for large correction to the lightest physical Higgs mass, the singlet's VEV explains why the $\hat{I}¼$ terms (for the Higgs doublets and the new triplets) are naturally of order the electroweak (EW) scale. We also show that singlet-triplet coupling significantly changes the RG evolution of the singlet mass squared, helping to render this mass squared negative, as required for the singlet to acquire a VEV. We analyze constrains on this scenario from EW precision measurements and find that a relatively large region of the parameter space of this model is viable, especially with the triplet fermions (including doubly-charged) being light.

31 pages, 6 figures, 2 tables. V2: minor corrections and references added