Acceleration of the Universe in Type-0 Non-Critical Strings: a Review

Abstract

I review cosmology within the framework of type-0 non-critical strings, proposed in collaboration with G. Diamandis, B. Georgalas, E. Papantonopoulos and I. Pappa. The instabilities of the tachyonic backgrounds, due to the absence of space-time supersymmetry, are treated in this framework as a necessary ingredient to ensure cosmological flow. The model involves D3 brane worlds, whose initial quantum fluctuations induce the non criticality. I argue that this model is compatible with the current astrophysical observations pointing towards acceleration of the Universe. A crucial r\^ole for the correct ``phenomenology'' of the model, in particular the order-one value of the deceleration parameter, is played by the relative magnitude of the flux of the five form of the type-0 string as compared to the size of the volume of five of the extra dimensions, transverse to the direction of the flux-field.