Branes and fluxes in orientifolds and K-theory Original Research Article

RR fields in string backgrounds including orientifold planes and branes on top of them are classified by K-theory. Following the idea introduced in , we also classify such fluxes by cohomology. Both of them are compared through the Atiyah–Hirzebruch spectral sequence. Some new correlations between branes on orientifold planes Op± and obstructions to the existence of some branes are found. Finally, we find a topological condition that avoid the presence of global gauge anomalies in lower-dimensional systems.