Relic gravitons from the pre-big bang: what we know and what we do not know

TL;DR

This paper reviews current understanding of relic gravitons potentially originating from a pre-big bang epoch, exploring theoretical motivations from string theory and highlighting gaps in knowledge about their properties and detectability.

Contribution

It provides a comprehensive overview of the theoretical background and current status of relic gravitons from the pre-big bang era, emphasizing the role of string theory dualities.

Findings

Relic gravitons may carry signatures of pre-big bang physics.

Current observational constraints limit the detectability of these gravitons.

Theoretical models suggest specific spectral features linked to string theory.

Abstract

I discuss the status of present knowledge about a possible background of relic gravitons left by an early, pre-big bang cosmological epoch, whose existence in the past of our Universe is suggested by the duality symmetries of string theory.