Physics

Gravitation

Astronomy

Dark energy

Gravitational redshift

Gravitational wave

Metric expansion of space

Speed of gravity

Geometry

Cosmology

Theoretical physics

Mathematics

Scalar (mathematics)

Classical mechanics

Universe

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.

Scalar Induced Gravitational Waves Review