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.
Friday, September 25, 2009
It has been known for some time that minimal SUSY SU(5) is ruled out because proton lifetimes are less than the measured limits (t_p >= 6.6 x 10^33 yrs). In arXiv:0909.4105 [hep-ph], Abel and Khoze propose that the MSSM is a magnetic Seiberg dual of an unknown electric theory. Such a proposal would explain why the supersymmetric Standard Model appears to unify but the proton does not decay. The authors put forward a number of possible dual GUTs that may provide a consistent UV completion of the minimal SU(5) model, for example with SU(11)xSp(1)^3 and SU(9)xSp(1)^3 symmetry.
Wednesday, September 16, 2009
In arXiv:0907.3048, Nicolai et al. investigate cosmological singularity resolution in the context of an E_10 coset model. E_10 is the Kac-Moody big brother of E_8, the exceptional Lie group that was all the rage not long ago. The authors conclude there is a 'de-emergence' of space-time near the singularity. They also discuss observables near the singularity where they mention that the conserved E_10 Noether charges do constitute an infinite set of observables and their expectation values remain well defined in the deep quantum regime where the E_10/K(E_10) coset model is expected to replace space-time quantum field theory.