Intersecting D5-brane models with massive vector-like leptons

TL;DR

This paper constructs non-supersymmetric intersecting D5-brane models that replicate the standard model's matter content, including neutrinos and Higgs, with realistic gauge couplings and mechanisms to avoid unwanted particles and symmetries.

Contribution

It introduces eight-stack D5-brane models with specific constraints ensuring realistic particle spectra and gauge couplings close to experimental values, addressing hierarchy and unwanted states.

Findings

Models include right-chiral neutrinos and Higgs doublets.

Gauge coupling ratios match experimental data.

Unwanted tachyons can be eliminated through parameter choices.

Abstract

We construct eight-stack intersecting D5-brane models, with an orbifold transverse space, that yield the (non-supersymmetric) standard model up to vector-like leptons. The matter includes right-chiral neutrinos and the models have the renormalisable Yukawa couplings to tachyonic Higgs doublets needed to generate 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 a string-scale mass via a generalised Green-Schwarz mechanism, and that there are no surviving, unwanted gauged U(1) symmetries coupled to matter. Gauge coupling constant ratios close to those measured are easily obtained for reasonable values of the parameters, consistently with having the string scale close to the electroweak scale, as required to avoid the hierarchy problem. Unwanted (colour-triplet, charged-singlet, and neutral-singlet) scalar tachyons can be removed by a suitable choice of the parameters.