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

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 errors 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 errors. 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.

Comments: 30 pages, 7 figures, accepted by JCAP, code available at https://github.com/xunjiexu/Unified-Bogoliubov.git