Prediction for $\alpha_3(M_z)$ in a string-inspired model

TL;DR

This paper uses two-loop renormalisation group equations to analyze an extended supersymmetric string-inspired model, showing it can match experimental strong coupling values without altering the unification scale.

Contribution

It provides an analytical two-loop RGE analysis of a string-inspired supersymmetric model with additional matter, predicting $oldsymbol{ ext{alpha}_3(M_z)}$ within experimental limits.

Findings

The model aligns with experimental $oldsymbol{ ext{alpha}_3(M_z)}$ values.

Heavy thresholds from extra matter are incorporated.

Unification scale remains similar to MSSM prediction.

Abstract

We apply the Renormalisation Group Evolution (RGE) to analyze the phenomenological implications of an extended supersymmetric model, for the value of the unification scale and the strong coupling at the electroweak scale. The model we consider is predicted to exist in Calabi-Yau string compactifications with Wilson line mechanism for $E_6$ symmetry breaking, contains additional matter beyond the MSSM spectrum and avoids the ``doublet-triplet'' splitting problem in the Higgs sector. The calculation is analytical in two-loop order and includes the effects of the heavy thresholds due to the additional matter considered. The value of $\alpha_3(M_z)$ can be brought within the experimental limits without a significant change of the unification scale from the MSSM prediction.