D-brane Deconstructions in IIB Orientifolds

TL;DR

<3-5 sentence high-level summary> The paper addresses how to systematically analyze D7-branes in Type IIB O3/O7 orientifolds, where generic D7s develop Whitney umbrella singularities that invalidate standard charge, moduli, and flux-counting formulas. It develops a unified framework using F-theory, perturbative IIB, and D9-anti-D9 tachyon condensation to derive corrected topological data, including the orientifold Euler characteristic χ_o(S) and the full D7 flux lattice, and verifies consistency across pictures. It also presents explicit constructions of open-string flux vacua via holomorphic curves and explains how brane recombination can generate worldvolume flux, with detailed open-string index calculations and stability considerations. The results provide a concrete, computable toolkit for D7 sectors in global IIB orientifolds, enabling more controlled model building and paving the way for statistical analyses of D7-flux vacua, while clarifying the limitations imposed by tadpole constraints and bulk-brane coupling.</3-5 sentence high-level summary>

Abstract

With model building applications in mind, we collect and develop basic techniques to analyze the landscape of D7-branes in type IIB compact Calabi-Yau orientifolds, in three different pictures: F-theory, the D7 worldvolume theory and D9-anti-D9 tachyon condensation. A significant complication is that consistent D7-branes in the presence of O7^- planes are generically singular, with singularities locally modeled by the Whitney Umbrella. This invalidates the standard formulae for charges, moduli space and flux lattice dimensions. We infer the correct formulae by comparison to F-theory and derive them independently and more generally from the tachyon picture, and relate these numbers to the closed string massless spectrum of the orientifold compactification in an interesting way. We furthermore give concrete recipes to explicitly and systematically construct nontrivial D-brane worldvolume flux vacua in arbitrary Calabi-Yau orientifolds, illustrate how to read off D-brane flux content, enhanced gauge groups and charged matter spectra from tachyon matrices, and demonstrate how brane recombination in general leads to flux creation, as required by charge conservation and by equivalence of geometric and gauge theory moduli spaces.