Acceleration of the Universe in Type-0 Non-Critical Strings

TL;DR

This paper discusses a non-critical string theory model involving D3 branes that can explain the universe's accelerated expansion and eventual exit from a de Sitter phase, aligning with current observations.

Contribution

It introduces a type-0 string theory model with non-criticality that accounts for cosmic acceleration and provides a potential mechanism for transitioning out of de Sitter space.

Findings

Model is compatible with current cosmological observations.

The flux of the five-form field influences the universe's phenomenology.

The model suggests a non-permanent de Sitter phase with a graceful exit.

Abstract

Presently there is preliminary observational evidence that the cosmological constant might be non zero, and hence that our Universe is eternally accelerating (de Sitter). This poses fundamental problems for string theory, since a scattering matrix is not well defined in such Universes. In a previous paper we have presented a model, based on (non-equilibrium) non-critical strings, which is characterized by eventual ``graceful'' exit from a de Sitter phase. The model is based on a type-0 string theory, involving D3 brane worlds, whose initial quantum fluctuations induce the non criticality. We argue in this article that this model is compatible with the current observations. A crucial r\^ole for the correct ``phenomenology'' of the model is played by the relative magnitude of the flux of the five form of the type 0 string to the size of five of the extra dimensions, transverse to the direction of the flux-field. We do not claim, at this stage at least, that this model is a realistic physical model for the Universe, but we find it interesting that the model cannot be ruled out immediately, at least on phenomenological grounds.