Robustness and Predictivity of 4 TeV Unification

Abstract

The stability of the predictions of two of the standard model parameters, ${\alpha }_3(M_Z)$ and ${\sin }^2\theta (M_Z)$, in a $M_U\sim 4$ TeV unification model is examined. It is concluded that varying the unification scale between $M_U\simeq 2.5$ TeV and $M_U\simeq 5$ TeV leaves robust all predictions within reasonable bounds. Choosing $M_U=3.8\pm 0.4$ TeV gives, at lowest order, accurate predictions at $M_Z$. The impact of threshold effects on unification depends on the spectrum of states beyond the standard model.

Comments: 16 pages LaTeX including 7 eps figures. New discussion of threshold effects with four new figures