Ramond-Ramond fields, fractional branes and orbifold differential K-theory

Richard J. Szabo, Alessandro Valentino

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9 Citations (Scopus)


We study D-branes and Ramond-Ramond fields on global orbifolds of Type II string theory with vanishing H-flux using methods of equivariant K-theory and K-homology. We illustrate how Bredon equivariant cohomology naturally realizes stringy orbifold cohomology. We emphasize its role as the correct cohomological tool which captures known features of the low-energy effective field theory, and which provides new consistency conditions for fractional D-branes and Ramond-Ramond fields on orbifolds. We use an equivariant Chern character from equivariant K-theory to Bredon cohomology to define new Ramond-Ramond couplings of D-branes which generalize previous examples. We propose a definition for groups of differential characters associated to equivariant K-theory. We derive a Dirac quantization rule for Ramond-Ramond fluxes, and study flat Ramond-Ramond potentials on orbifolds. © Springer-Verlag 2009.

Original languageEnglish
Pages (from-to)647-702
Number of pages56
JournalCommunications in Mathematical Physics
Issue number3
Publication statusPublished - Jan 2010


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