Exact Standard Model Compactifications from Intersecting Branes

TL;DR

This paper constructs non-supersymmetric intersecting D6-brane models that exactly reproduce the Standard Model spectrum, including right-handed neutrinos, with mechanisms for anomaly cancellation and proton stability.

Contribution

It presents explicit string theory models with intersecting D6-branes that realize the Standard Model spectrum and gauge symmetries, including mechanisms for anomaly cancellation and mass generation.

Findings

Exact Standard Model spectrum from D6-brane configurations

Proton stability due to gauged baryon number

Neutrinos are Dirac particles with small masses

Abstract

We construct six stack D6-brane vacua (non-supersymmetric) that have at low energy exactly the standard model (with right handed neutrinos). The construction is based on D6-branes intersecting at angles in $D = 4$ type toroidal orientifolds of type I strings. Three U(1)'s become massive through their couplings to RR fields and from the three surviving massless U(1)'s at low energies, one is the standard model hypercharge generator. The two extra massless U(1)'s get broken, as suggested recently (hep-th/0205147), by requiring some intersections to respect N=1 supersymmetry thus supporting the appearance of massless charged singlets. Proton and lepton number are gauged symmetries and their anomalies are cancelled through a generalized Green-Schwarz mechanism that gives masses to the corresponding gauge bosons through couplings to RR fields. Thus proton is stable and neutrinos are of Dirac type with small masses as a result of a PQ like-symmetry. The models predict the existence of only two supersymmetric particles, superpartners of $\nu_R$'s.