A new scenario for string unification

Abstract

We present a new scenario for gauge coupling unification in flipped SU(5) string models, which identifies the $M_{32}$ scale of SU(3) and SU(2) unification with the empirical $M_{\mathrm{LEP}}\sim 10^{15-16}$~GeV scale, and the $M_{51}$ scale of SU(5) and U(1) unification with the theoretical $M_{\mathrm{string}}\sim 5\times 10^{17}$~GeV string unification scale. The vacuum shift necessary for the cancellation of the anomalous ${\mathrm{U}}_{\mathrm{A}}(1)$ and an SU(4) hidden sector with fractionally-charged particles, play a crucial role in the dynamical determination of all intermediate mass scales in this scenario.

Comments: 8 pages, LaTeX, 2 figures (uuencoded)