Initial Conditions in Pre-Big Bang

TL;DR

This paper discusses the initial conditions required for pre-big bang cosmology, emphasizing the need for a smooth, flat universe at the start of dilaton-driven inflation, and compares it with standard inflation.

Contribution

It highlights the fine-tuning problem in pre-big bang models and provides numerical limits on initial conditions, contrasting with standard inflation.

Findings

Pre-big bang requires a smooth, flat universe at the onset of inflation.

Numerical limits on initial conditions are established.

Differences between pre-big bang and standard inflation are clarified.

Abstract

This note is a summary of the work reported in hep-th/9801073. We give a brief discussion of the fine tuning problem in pre-big bang cosmology. We use the flatness problem as our test case, and in addition to the exact numerical limits on initial conditions, we highlight the differences between pre-big bang and standard inflation. The main difference is that in pre-big bang the universe must be smooth and flat in an exponentially large domain already at the beginning of the dilaton-driven inflation.