Scalar Induced Gravitational Waves Review

We provide a review on the state-of-the-art of gravitational waves induced by primordial fluctuations, so-called induced gravitational waves. We present the intuitive physics behind induced gravitational waves and we revisit and unify the general analytical formulation. We then present general formulas in a compact form, ready to be applied. This review places emphasis on the open possibility that the primordial universe experienced a different expansion history than the often assumed radiation dominated cosmology. We hope that anyone interested in the topic will become aware of current advances in the cosmology of induced gravitational waves, as well as becoming familiar with the calculations behind.

Automated summary

This review provides an overview of gravitational waves induced by primordial fluctuations, focusing on the intuitive physics and general analytical formulation behind induced gravitational waves. It suggests the open possibility of a different expansion history in the primordial universe than the commonly assumed radiation dominated cosmology, and aims to raise awareness of current advances in the cosmology of induced gravitational waves.