Novel Extension of MSSM and ``TeV Scale'' Coupling Unification

TL;DR

This paper proposes a novel extension of the MSSM to achieve gauge coupling unification at a TeV-scale $M_s$ while preserving one-loop precision analogous to the MSSM. The construction adds vector-like singlets $F_\pm$ with hypercharge $\pm 2$ and promotes the model to ${\cal N}=2$ on a KK tower, with a ${\bf Z}_2$ orbifold yielding a light ${\cal N}=1$ spectrum and heavy ${\cal N}=2$ KK states; unification proceeds via KK threshold corrections characterized by ${\widetilde{b}}_a$ and a universal ratio $\nu_{ab}=1$. A lower bound on $M_s$ depends on the number of heavy flavors $n_f$, giving $M_s \gtrsim 10^9$ GeV for $n_f=3$ but allowing TeV-scale unification for $n_f=2$, in which case the light $F_\pm$ could be experimentally accessible if $M_F \sim M_H$. Higher-loop corrections are argued to be under control in a supersymmetric, KK-threshold–dominated regime, though a fully explicit string vacuum remains to be constructed; the authors outline brane-world embeddings, Voisin-Borcea orbifolds, and potential twisted-sector states as avenues to realize the model. Overall, the work offers a coherent framework in which MSSM-like unification is explained without invoking a superheavy desert and yields testable predictions for near-future collider experiments.

Abstract

Motivated by the coupling unification problem, we propose a novel extension of the Minimal Supersymmetric Standard Model. One of the predictions of this extension is existence of new states neutral under SU(3)_c X SU(2)_w but charged under U(1)_Y. The mass scale for these new states can be around the mass scale of the electroweak Higgs doublets. This suggests a possibility of their detection in the present or near future collider experiments. Unification of gauge couplings in this extension is as precise (at one loop) as in the MSSM, and can occur in the TeV range.