A Minimal Superstring Standard Model I: Flat Directions

TL;DR

This paper explores flat directions in a string-derived model that reduce to the MSSM, showing that the model can naturally produce the minimal spectrum while maintaining phenomenological viability.

Contribution

It identifies multiple flat directions in a string model that yield the MSSM spectrum, demonstrating the model's flexibility in satisfying phenomenological constraints.

Findings

Multiple flat directions produce the MSSM spectrum.

Exotic states can be decoupled while satisfying phenomenological constraints.

The model retains sufficient freedom after imposing flatness conditions.

Abstract

Three family SU(3)_C x SU(2)_L x U(1)_Y string models in several constructions generically possess two features: (i) an extra local anomalous U(1)_A and (ii) numerous (often fractionally charged) exotic particles beyond those in the minimal supersymmetric model (MSSM). Recently, we demonstrated that the observable sector effective field theory of such a free fermionic string model can reduce to that of the MSSM, with the standard observable gauge group being just SU(3)_C x SU(2)_L x U(1)_Y and the SU(3)_C x SU(2)_L x U(1)_Y-charged spectrum of the observable sector consisting solely of the MSSM spectrum. An example of a model with this property was shown. We continue our investigation of this model by presenting a large set of different flat directions of the same model that all produce the MSSM spectrum. Our results suggest that even after imposing the conditions for the decoupling of exotic states, there may remain sufficient freedom to satisfy the remaining phenomenological constraints imposed by the observed data.