Dirichlet Branes on Orbifolds

TL;DR

This work systematically analyzes D-branes on ${\mathbb Z_2}$ orbifolds of toroidally compactified Type II string theories using boundary conformal field theory and K-theory. It identifies the full D-brane spectrum (fractional, bulk, and truncated) and shows precise agreement between boundary-state constructions and K-theory classifications in both uncompactified and toroidally compactified settings. The authors compute twisted and untwisted R-R charge densities, derive descent relations between branes, and fix overall normalizations by matching open-string and field-theory amplitudes. The results highlight that D-brane charge lattices in these orbifolds can be larger than cohomology yet remain of maximal rank, and they hold for supersymmetric as well as non-supersymmetric theories, suggesting deep topological underpinnings of D-brane charge beyond SUSY.

Abstract

The D-brane spectrum of a class of $\Zop_2$ orbifolds of toroidally compactified Type IIA and Type IIB string theory is analysed systematically. The corresponding K-theory groups are determined and complete agreement is found. The charge densities of the various branes are also calculated.