Improving the tunings of the MSSM by adding triplets and singlet

TL;DR

This paper extends the MSSM by adding triplets and a singlet to address the little hierarchy and μ problems, showing how their interactions improve Higgs mass corrections and electroweak scale naturalness.

Contribution

It introduces a combined triplet and singlet extension of the MSSM that solves hierarchy and μ problems simultaneously, with detailed RG and phenomenological analysis.

Findings

Triplet addition raises the lightest Higgs mass effectively.

Singlet's VEV is naturally at the electroweak scale due to RG effects.

Parameter space with light triplet fermions is consistent with precision measurements.

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 $\mu$ 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 $\mu$ 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.