In the recent arXiv:0906.5135, Saridakis and Ward propose a novel dark energy candidate, based on the dynamics of ghost D-branes in compactified Type II string theory. This is an approach which is based on open string dynamics that envisions a post-inflation universe living on branes that wrap cycles in the compact space, with the GUT or Electro-Weak phase transition manifested geometrically.
Ghost D-branes are defined as Dp-branes with a Z_2 symmetry that can flip the signs of the NS-NS and RR sectors (arXiv:0601024[hep-th]). By using ghost D-branes, the authors are able to recover an effective dark energy behaving either as quintessence or as a phantom field, without the need of orientifolds.
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