Chapter 6: Quantum Mechanics of Relic Gravitons

Gravitational wave astronomy does not demand a quantum treatment since it successfully assumes a classical description of the tensor modes of the geometry and while this picture is not challenged by any direct observation, the purpose of this chapter is to motivate the quantum mechanical analysis which is mandatory in the case of the relic gravitons. The Universe evolves classically for most of its history but its inhomogeneities may have a quantum mechanical origin and this perspective is justified in all the situations where the classical inhomogeneities either vanish or, for some reason, are strongly suppressed. Most of the topics discussed hereunder involve the conditions under which the quantum treatment of the large-scale inhomogeneities is essential…