Saturday, September 26, 2009

Dark Energy and Ghost D-Branes

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

The MSSM as a Magnetic Seiberg Dual

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

Quantum Cosmological Billiards

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.