Unification and fermion mass relations in low string scale D-brane models

Abstract

In this talk, gauge coupling evolution is analyzed in D-brane inspired models with two Higgs doublets and a U(3) × U(2) × U(1)N gauge symmetry. In particular, we focus on D-brane configurations with two or three abelian factors. We find that the correct hypercharge assignment of the Standard Model particles is reproduced for six viable models distinguished by different brane configurations. We also investigate the bottom tau quark mass relation and find that the correct low energy mb/mτ ratio is obtained for equal b − τ Yukawa couplings at a string scale around 103 TeV.