Thesis: Orientifolds, Anomalies and the Standard Model

TL;DR

This thesis explores D-brane orientifold models of the Standard Model, analyzing anomaly cancellation, mass spectra, and phenomenological implications of extra U(1) gauge fields in non-supersymmetric string constructions.

Contribution

It provides a detailed analysis of anomaly cancellation, mass generation, and phenomenological constraints in orientifold models with broken supersymmetry.

Findings

Green-Schwarz mechanism cancels anomalies and gives mass to U(1) gauge fields.

Higher-dimensional anomalies influence the masses of anomalous U(1)s.

Constraints on string scale arise from contributions to anomalous moments.

Abstract

In this thesis, we study aspects of D-brane realizations of the Standard Model. Specifically, we study orientifold models with rotation and translation elements that break supersymmetry, provide the general consistency conditions and derive the massless spectrum for these type of orientifolds. These models contain in general anomalous U(1) gauge fields. The Green-Schwarz mechanism cancels the anomaly and provides a mass term for the anomalous gauge fields. We calculate the bare mass for supersymmetric and non-supersymmetric vacua and we show that higher dimensional anomalies can affect the masses of the anomalous U(1)s. Phenomenological aspects are also discussed. We evaluate the contribution of the extra U(1) fields to the anomalous moments and it is shown that this imposes constraints on the magnitude of the string scale.