Cosmological Perturbations in Double Field Theory

TL;DR

This paper investigates cosmological perturbations within double field theory, addressing consistency issues, duality symmetries, and proposing a gauge-invariant framework for analyzing scalar, vector, and tensor modes in a string-inspired cosmological setting.

Contribution

It provides a consistent perturbative analysis of double field theory on cosmological backgrounds, including a generalized decomposition and gauge-invariant variables for cosmological perturbations.

Findings

Double field theory encodes both momentum and winding modes in cosmological backgrounds.

Fewer tensor modes but more scalar and vector modes compared to standard cosmology.

Proposes a gauge-invariant framework for cosmological perturbations in double field theory.

Abstract

We explore perturbative double field theory about time-dependent (cosmological) backgrounds to cubic order. To this order the theory is consistent in a weakly constrained sense, so that for a toroidal geometry it encodes both momentum and genuine winding modes. We give a self-contained discussion of the consistency problems and their resolution, including the role of cocycle factors and the $O(d,d,\mathbb{Z})$ duality. Finally, as a first step toward the computation of cosmological correlation functions, we propose a generalized scalar-vector-tensor decomposition and use it to construct gauge invariant generalized Bardeen variables. Compared to standard cosmology there are fewer tensor modes but more vector and scalar modes.