Second-order Gauge-invariant Cosmological Perturbation Theory: Current Status

TL;DR

This paper reviews the current state of second-order gauge-invariant cosmological perturbation theory, focusing on a universe with a scalar field, and discusses future challenges and applications to non-Gaussianity in CMB observations.

Contribution

It provides a comprehensive review of recent developments in second-order gauge-invariant cosmological perturbation theory, highlighting key problems and future directions.

Findings

Identifies unresolved issues in the theoretical framework.

Emphasizes relevance to non-Gaussianity predictions in CMB.

Suggests potential for improved comparison with observations.

Abstract

The current status of the recent developments of the second-order gauge-invariant cosmological perturbation theory is reviewed. To show the essence of this perturbation theory, we concentrate only on the universe filled with a single scalar field. Through this review, we point out the problems which should be clarified for the further theoretical sophistication of this perturbation theory. We also expect that this theoretical sophistication will be also useful to discuss the theoretical predictions of Non-Gaussianity in CMB and comparison with observations.