The String Coupling Accelerates the Expansion of the Universe

TL;DR

This paper proposes that in non-critical string cosmology, the universe's acceleration is driven by the string coupling, which influences the deceleration parameter and predicts an accelerating expansion consistent with observations.

Contribution

It introduces a model linking string coupling dynamics to cosmic acceleration, providing a novel explanation within string theory frameworks.

Findings

Deceleration parameter Q_0 is proportional to the negative of g_s^2.

The observed Q_0 suggests g_s^2 ~ 0.6.

String coupling approaches zero at large times, indicating asymptotic freedom.

Abstract

Generic cosmological models in non-critical string theory have a time-dependent dilaton background at a late epoch. The cosmological deceleration parameter Q_0 is given by the square of the string coupling, g_s^2, up to a negative sign. Hence the expansion of the Universe must accelerate eventually, and the observed value of Q_0 coresponds to g_s^2 ~ 0.6. In this scenario, the string coupling is asymptotically free at large times, but its present rate of change is imperceptibly small.