On the Gauge Invariance of Cosmological Gravitational Waves

TL;DR

This paper examines the gauge invariance of cosmological gravitational waves, focusing on their production, propagation, and measurement in the early universe at second-order perturbation theory.

Contribution

It provides a comprehensive analysis of gauge invariance issues for gravitational waves across different stages in the early universe.

Findings

Clarifies the gauge invariance during gravitational wave production

Analyzes the propagation effects in the real universe

Discusses measurement implications for gauge-invariant signals

Abstract

The issue of the gauge invariance of gravitational waves arises if they are produced in the early universe at second-order in perturbation theory. We address it by dividing the discussion about the gauge invariance in three parts: the production of gravitational waves, their propagation in the real universe, and their measurement.