The fine tuning problem in pre-big-bang inflation

TL;DR

This paper investigates how spatial curvature and string theory corrections influence pre-big-bang inflation, showing that they can produce sufficient inflation to address cosmological problems while remaining consistent with observational constraints.

Contribution

It demonstrates that $O(\alpha ')$ corrections induce a long inflationary phase in pre-big-bang models, compatible with observational data, regardless of initial curvature conditions.

Findings

$O(\alpha ')$ corrections lead to exponential inflation.

Inflation duration can solve horizon and flatness problems.

Model remains consistent with COBE, pulsar timing, and nucleosynthesis constraints.

Abstract

We examine the effect of spatial curvature in the pre-big-bang inflationary model suggested by string theory. We study $O(\alpha ')$ corrections and we show that, independently of the initial curvature, they lead to a phase of exponential inflation. The amount of inflation in this phase is long enough to solve the horizon and flatness problems if the evolution starts deeply into the weak coupling regime. There is a region of the parameter space of the model where such a long inflationary phase at the string scale is consistent with COBE anisotropies, millisecond pulsar timing and nucleosynthesis constraints. We discuss implications for the spectrum of relic gravitational waves at the frequencies of LIGO and Virgo.