A Unified Bogoliubov Approach to Primordial Gravitational Waves: From Inflation to Reheating

TL;DR

This paper introduces an improved numerical method based on the Bogoliubov approach to accurately compute the full spectrum of primordial gravitational waves from inflation to reheating, addressing previous numerical challenges.

Contribution

The authors develop a robust numerical technique with analytical insights that captures high-frequency gravitational wave features influenced by inflaton oscillations.

Findings

The method overcomes numerical instabilities at high frequencies.

Anharmonic inflaton oscillations affect the high-frequency GW spectrum.

The code is publicly available on GitHub.

Abstract

We present an effective numerical method that can be used to straightforwardly calculate the full spectrum of primordial gravitational waves produced during inflation and reheating. Our method is based on the Bogoliubov approach with several key improvements to overcome its shortcomings such as numerical instabilities at high frequencies and issues with tachyonic modes. We also present a few useful analytical examples from which one can gain crucial insights into the numerical instabilities. The improved method allows us to demonstrate that anharmonicity of inflaton oscillations can leave interesting fingerprints on the high-frequency part of the GW spectrum. Our numerical code is publicly available on GitHub https://github.com/xunjiexu/Unified-Bogoliubov.git.