Pre-Big-Bang Inflation Requires Fine Tuning

TL;DR

The paper demonstrates that pre-big-bang inflation models inspired by superstring theories require fine-tuning of initial conditions due to the impact of spatial curvature, which limits their ability to solve fundamental cosmological problems.

Contribution

It provides a detailed analysis of how spatial curvature affects pre-big-bang inflation in both Jordan and Einstein frames, highlighting the need for fine-tuning.

Findings

Spatial curvature reduces inflation duration significantly.

Both positive and negative curvature have similar effects.

Fine-tuning is necessary for pre-big-bang models to solve cosmological problems.

Abstract

The pre-big-bang cosmology inspired by superstring theories has been suggested as an alternative to slow-roll inflation. We analyze, in both the Jordan and Einstein frames, the effect of spatial curvature on this scenario and show that too much curvature --- of either sign --- reduces the duration of the inflationary era to such an extent that the flatness and horizon problems are not solved. Hence, a fine-tuning of initial conditions is required to obtain enough inflation to solve the cosmological problems.