Standard Model at Intersecting D5-branes: Lowering the String Scale

TL;DR

This paper constructs explicit Type IIB D5-brane models with a Standard Model spectrum, allowing for a low string scale around 1-10 TeV, which could address the hierarchy problem while maintaining proton stability.

Contribution

It generalizes previous D6-brane models to D5-branes on T^4 imes (C/Z_N), achieving a SM-like spectrum with a low string scale and no supersymmetry.

Findings

Explicit D5-brane models with SM spectrum and low string scale.

Automatic proton stability due to gauged baryon number.

Models with N=0 SUSY in bulk and on branes.

Abstract

Recently a class of Type IIA orientifold models was constructed yielding just the fermions of the SM at the intersections of D6-branes wrapping a 6-torus. We generalize that construction to the case of Type IIB compactified on an orientifold of T^4 \times (C/Z_N) with D5-branes intersecting at angles on T^4. We construct explicit models in which the massless fermion spectrum is just the one of a three-generation Standard Model. One of the motivations for these new constructions is that in this case there are 2 dimensions which are transverse to the SM D5-brane configuration. By making those two dimensions large enough one can have a low string scale M_s of order 1-10 TeV and still have a large M_{Planck} in agreement with observations. From this point of view, these are the first explicit D-brane string constructions where one can achieve having just the fermionic spectrum and gauge group of the SM embedded in a Low String Scale scenario. The cancellation of U(1) anomalies turns out to be quite analogous to the toroidal D6-brane case and the proton is automatically stable due to the gauging of baryon number. Unlike the D6-brane case, the present class of models has N = 0 SUSY both in the bulk and on the branes and hence the spectrum is simpler.