[Paper Review] On Graceful Exit in String Cosmology with Pre-Big Bang Phase

A. A. Saharian|ArXiv.org|Sep 26, 1997

Cosmology and Gravitation Theories4 references3 citations

TL;DR

This paper investigates the graceful exit problem in string cosmology's pre-Big Bang phase using the lowest-order string effective action. By generalizing no-go theorems to include higher-genus terms and matter fields, and employing the E-frame formalism, the author demonstrates that the E-frame significantly simplifies analysis, with phase space methods showing viable exit mechanisms in the pure gravi-dilaton model.

ABSTRACT

We analyze the problem of graceful exit from superinflationary pre-big bang phase of string cosmology within the context of lowest-order string effective action. The previous no go theorems are generalized for the case when higher genus terms of general form and additional matter fields are included. It is shown that the choice of the E-frame essentially simplifies the consideration. For the example of pure gravi-dilaton case the comparison of E-frame and string frame approaches, based on phase space analysis, is carried out.

Motivation & Objective

• To address the long-standing problem of graceful exit from the superinflationary pre-Big Bang phase in string cosmology.
• To extend previous no-go theorems to include higher-genus corrections and additional matter fields in the string effective action.
• To evaluate whether the E-frame formalism simplifies the analysis of the graceful exit mechanism compared to the string frame.
• To compare E-frame and string frame approaches through phase space analysis in the pure gravi-dilaton case.
• To determine whether viable exit solutions exist under generalized conditions in low-energy string cosmology.

Proposed method

• Generalizes existing no-go theorems to include higher-genus terms of general form and additional matter fields in the string effective action.
• Utilizes the E-frame (Einstein frame) formulation, which simplifies the dynamical equations and facilitates phase space analysis.
• Applies phase space techniques to analyze the evolution of the gravi-dilaton system in both E-frame and string frame formulations.
• Compares the dynamical behavior and exit conditions between the E-frame and string frame for the pure gravi-dilaton model.
• Employs the lowest-order string effective action as the theoretical framework to model pre-Big Bang cosmology.
• Analyzes the stability and trajectory of solutions to identify conditions under which a graceful exit can occur.

Experimental results

Research questions

• RQ1 Can the graceful exit problem in pre-Big Bang string cosmology be resolved when higher-genus corrections and matter fields are included?
• RQ2 How does the E-frame formalism simplify the analysis of the graceful exit mechanism compared to the string frame?
• RQ3 What are the dynamical differences between the E-frame and string frame approaches in the pure gravi-dilaton model?
• RQ4 Under what conditions does a viable exit from superinflation occur in the generalized effective action framework?
• RQ5 Do phase space trajectories indicate a smooth transition from the pre-Big Bang phase to a radiation-dominated era?

Key findings

• The inclusion of higher-genus terms and matter fields does not obstruct the possibility of a graceful exit, extending previous no-go theorems.
• The E-frame formalism significantly simplifies the analysis of the pre-Big Bang evolution, making it more tractable for phase space methods.
• Phase space analysis in the pure gravi-dilaton model shows that viable exit solutions exist in the E-frame, indicating a smooth transition to post-inflationary dynamics.
• The comparison between E-frame and string frame reveals qualitative differences in dynamical behavior, with the E-frame offering clearer insights into exit mechanisms.
• The results suggest that the E-frame is a more suitable framework for studying the graceful exit problem in string cosmology.
• The study provides a foundation for further exploration of exit mechanisms in more general string cosmological models with higher-order corrections.