Cosmological Structure Problem of the Pre-Big Bang Scenario

TL;DR

This paper calculates the density and gravitational wave spectra in a string cosmology pre-big bang scenario, finding significant deviations from observed large-scale structure spectra, thus questioning its viability for explaining current observations.

Contribution

It provides detailed spectral predictions for density and gravitational waves in the pre-big bang string cosmology model, highlighting discrepancies with observational data.

Findings

Spectra are tilted with n ~ 4 and n_T ~ 3, differing from observed values.

Pre-big bang scenario may not generate observable large-scale structures.

Quantum corrections might be necessary for better agreement.

Abstract

We calculate the density and gravitational wave spectrums generated in a version of string cosmology termed pre-big bang scenario. The large scale structures are originated from quantum fluctuations of the metric and dilaton field during a pole-like inflation stage driven by a potential-less dilaton field realized in the low-energy effective action of string theory. The generated classical density field and the gravitational wave in the second horizon crossing epoch show tilted spectrums with n ~ 4 and n_T ~ 3, respectively. These differ from the observed spectrum of the large angular scale anisotropy of the cosmic microwave background radiation which supports scale invariant ones with n ~ 1 and n_T ~ 0. This suggests that the pre-big bang stage is not suitable for generating the present day observable large scale structures, and suggests the importance of investigating the quantum generation processes during stringy era with higher order quantum correction terms.