TASI Lectures: Particle Physics from Perturbative and Non-perturbative Effects in D-braneworlds

TL;DR

The notes survey how type II orientifold compactifications realize realistic four-dimensional physics via spacetime-filling D-branes, with gauge groups and chiral matter arising at brane intersections and family structure set by intersection numbers. They emphasize global consistency through RR tadpole cancellation and the generalized Green-Schwarz mechanism, and show how non-perturbative D-instantons can generate otherwise forbidden superpotential couplings, impacting neutrino masses and top-quark Yukawas. The discussion blends a geometric IIa perspective (D6-branes, toroidal orbifolds, quivers) with CFT tools and touches on IIb/GUT-F-theory connections, highlighting the role of instanton zero modes in determining allowed non-perturbative effects. The bottom-up quiver approach is proposed as a practical strategy to constrain the vast string landscape while preserving key phenomenological features and consistency requirements.

Abstract

In these notes we review aspects of semi-realistic particle physics from the point of view of type II orientifold compactifications. We discuss the appearance of gauge theories on spacetime filling D-branes which wrap non-trivial cycles in the Calabi-Yau. Chiral matter can appear at their intersections, with a natural interpretation of family replication given by the topological intersection number. We discuss global consistency, including tadpole cancellation and the generalized Green-Schwarz mechanism, and also the importance of related global $U(1)$ symmetries for superpotential couplings. We review the basics of D-instantons, which can generate superpotential corrections to charged matter couplings forbidden by the global $U(1)$ symmetries and may play an important role in moduli stabilization. Finally, for the purpose of studying the landscape, we discuss certain advantages of studying quiver gauge theories which arise from type II orientifold compactifications rather than globally defined models. We utilize the type IIa geometric picture and CFT techniques to illustrate the main physical points, though sometimes we supplement the discussion from the type IIb perspective using complex algebraic geometry.