Graviton Spectra in String Cosmology

TL;DR

This paper predicts a distinctive peak in the primordial graviton spectrum caused by a bounce in the early universe, which could be detected by future interferometers, providing evidence for string cosmology.

Contribution

It introduces a novel feature in the graviton spectrum resulting from a bounce in string cosmology, analytically and numerically characterizing its properties.

Findings

Peak in graviton spectrum predicted during bounce era

Peak frequency and intensity estimated for detection

Detection would support string cosmology models

Abstract

We propose to uncover the signature of a stringy era in the primordial Universe by searching for a prominent peak in the relic graviton spectrum. This feature, which in our specific model terminates an $\omega^3$ increase and initiates an $\omega^{-7}$ decrease, is induced during the so far overlooked bounce of the scale factor between the collapsing deflationary era (or pre-Big Bang) and the expanding inflationary era (or post-Big Bang). We evaluate both analytically and numerically the frequency and the intensity of the peak and we show that they may likely fall in the realm of the new generation of interferometric detectors. The existence of a peak is at variance with ordinarily monotonic (either increasing or decreasing) graviton spectra of canonical cosmologies; its detection would therefore offer strong support to string cosmology.