Intersecting D5-brane models with massive vector-like leptons

We construct eight-stack intersecting D5-brane models, with an orbifoldtransverse space, that yield the (non-supersymmetric) standard model up tovector-like leptons. The matter includes right-chiral neutrinos and the modelshave the renormalisable Yukawa couplings to tachyonic Higgs doublets needed togenerate mass terms for {\it all} matter, including the vector-like leptons.The models are constrained by the requirement that twisted tadpoles cancel,that the gauge boson coupled to the weak hypercharge $U(1)_Y$ does not get astring-scale mass via a generalised Green-Schwarz mechanism, and that there areno surviving, unwanted gauged U(1) symmetries coupled to matter. Gauge coupling constant ratios close to those measured are easily obtainedfor reasonable values of the parameters, consistently with having the stringscale close to the electroweak scale, as required to avoid the hierarchyproblem. Unwanted (colour-triplet, charged-singlet, and neutral-singlet) scalartachyons can be removed by a suitable choice of the parameters.Comment: 15 pages, LaTeX fil