Standard Model Compactifications from Intersecting Branes

TL;DR

Problem: constructing four-dimensional, non-supersymmetric string models that realize the Standard Model at low energy and address neutrino masses within intersecting D6-brane frameworks. Approach: propose a four-stack PS-like GUT on an orientifolded $T^6$ with intersecting branes, requiring extra $U(1)$ branes for RR tadpole cancellation, and enforce $N=1$ SUSY in selected sectors to generate gauge-singlet scalars and Majorana masses for nu_R, enabling a see-saw. Key results: the PS-A type model yields SM at low energy, with electroweak Yukawa couplings giving Dirac masses, $m_d = m_e$ relations, Majorana masses for nu_R, and a mechanism to break extra $U(1)$ via a generalized Green-Schwarz mechanism. Significance: demonstrates concrete, non-supersymmetric string realizations of the SM at low energy, including neutrino mass generation and anomaly-free $U(1)$ breaking, and provides a path to further GUT constructions from intersecting branes.

Abstract

We discuss the construction of four dimensional non-supersymmetric models obtained from configurations of D6-branes intersecting at angles. We present the first examples of string GUT models which break exactly to the Standard Model (SM) at low energy. Even though the models are non supersymmetric (SUSY), the demand that some open string sectors preserve N=1 SUSY creates gauge singlet scalars that break the extra anomaly free U(1)'s generically present in the models, predicting $s{\tilde ν}_R$'s and necessarily creating Majorana mass terms for right handed neutrinos.