Stability Analysis of the Cosmological Dynamics of $O(D,D)$-complete Stringy Gravity

TL;DR

This paper analyzes the stability and dynamics of cosmological solutions in $O(D,D)$-symmetric string theory, extending Einstein equations and exploring conditions for acceleration in a stringy gravity framework.

Contribution

It derives the autonomous form of $O(D,D)$-complete Friedmann equations, identifies critical points, and analyzes their stability, including phase portraits and cosmological implications.

Findings

Identification of critical points in the $O(D,D)$-symmetric cosmological system

Stability conditions for accelerating phases in string-inspired cosmology

Comparison of scalar field, radiation, and matter cases with Chameleon models

Abstract

The massless fields in the universal NS-NS sector of string theory form $O(D, D)$ multiplets of Double Field Theory, which is a theory that provides a T-duality covariant formulation of supergravity, leading to a stringy modification of General Relativity. In this framework, it is possible to write down the extensions of the Einstein field equations and the Friedmann equations in such a way that the coupling of gravitational and matter sectors is dictated by the $O(D, D)$ symmetry universally. In this paper, we obtain the autonomous form of the $O(D, D)$-complete Friedmann equations, find the critical points and perform their stability analysis. We also include the phase portraits of the system. Cosmologically interesting cases of scalar field, radiation, and matter are separately considered and compared with the Chameleon models in a similar setting. Accelerating phases and the conditions for their existence are also given for such cases.