Gravitational Waves from the Big Bang

TL;DR

This paper explores the potential of gravitational waves to provide direct observational evidence of the universe's earliest moments, focusing on signals from cosmic inflation detectable by NANOGrav.

Contribution

It investigates how primordial gravitational waves from cosmic inflation could explain signals observed by NANOGrav, advancing understanding of the early universe.

Findings

Gravitational waves offer a new window into the primordial universe.

The NANOGrav signals could originate from inflationary gravitational waves.

The study links gravitational wave signals to early universe cosmology.

Abstract

For millennia, humanity has relied exclusively on light$\unicode{x2014}$initially visible light and, later, broader and broader portions of the electromagnetic spectrum$\unicode{x2014}$to observe the universe. In the past decade, a remarkable chapter in extending astronomy beyond electromagnetic antennas has been concretized: the dawn of gravitational-wave astronomy has opened a new observational window into the cosmos. Among the many new astronomical sources we may now look for and study through their gravitational-wave signals, the Big Bang is surely among the most fascinating. Gravitational waves give us concrete hope of directly observing the primordial universe, whose light, emitted more than 13.7 billion years ago, is blocked from reaching our telescopes. This dissertation is aimed at the study of gravitational waves from cosmic inflation, the main scientific paradigm for the very early universe. Therefore, the text is divided into chapters on gravitational waves, inflationary cosmology, and inflationary gravitational waves. More specifically, our discussion will be steered by the endeavor to explain how the gravitational-wave signal sought by the NANOGrav observatory could have originated in the primordial universe.