Effects of anisotropy and spatial curvature on the pre-big bang scenario

TL;DR

This paper explores how anisotropy and spatial curvature influence the pre-big bang cosmological scenario within vacuum Brans-Dicke theory, identifying conditions that enable or prevent inflation.

Contribution

It provides exact anisotropic solutions including Bianchi types and FRW models, analyzing the impact of curvature and anisotropy on inflation in the pre-big bang context.

Findings

Large anisotropy and curvature can prevent inflation in certain parameter regimes.

Conditions for successful pre-big bang inflation are more restrictive with anisotropy and curvature.

Initial states generally resemble gravitational plane waves.

Abstract

A class of exact, anisotropic cosmological solutions to the vacuum Brans-Dicke theory of gravity is considered within the context of the pre-big bang scenario. Included in this class are the Bianchi type III, V and VI_h models and the spatially isotropic, negatively curved Friedmann-Robertson-Walker universe. The effects of large anisotropy and spatial curvature are determined. In contrast to negatively curved Friedmann-Robertson-Walker model, there exist regions of the parameter space in which the combined effects of curvature and anisotropy prevent the occurrence of inflation. When inflation is possible, the necessary and sufficient conditions for successful pre-big bang inflation are more stringent than in the isotropic models. The initial state for these models is established and corresponds in general to a gravitational plane wave.