In this thesis the relative spectral energy density of stochastic primordial gravitational waves is investigated. Decoupling of Standard Model particles and neutrino free-streaming affect the...Show moreIn this thesis the relative spectral energy density of stochastic primordial gravitational waves is investigated. Decoupling of Standard Model particles and neutrino free-streaming affect the expansion history of the universe and thus leave characteristic signatures on the amplitude of the gravitational wave spectrum. Adding extra light or heavy particles damps the spectrum at frequencies before the particle decouples. Including an extra neutrino species amplifies the spectrum at larger wave numbers, but damps it at shorter wave numbers. Measuring these primordial gravitational waves reveals the thermal history of the universe. One possible non-standard thermal history is early matter domination due to the inflaton. It is shown that, in this cosmology, the end of early matter domination and beginning of the radiation era depend linearly on the reheating temperature.Show less
In Cosmology, the theories of General Relativity and Quantum Mechanics have to work together very closely. However, the workings of quantum fields in General Relativity are challenging to calculate...Show moreIn Cosmology, the theories of General Relativity and Quantum Mechanics have to work together very closely. However, the workings of quantum fields in General Relativity are challenging to calculate, especially the backreaction of particle production caused by gravitational fields. This can normally only be calculated perturbatively. The theory of Classical-Quantum Correspondence could help with these calculations, as it allows for a single set of equations that covers the full evolution of both fields without the need for perturbations. This is possible by transforming the expectation values of the quantum field to depend on a corresponding classical one. This thesis focuses on the validation this theory of the Classical-Quantum Correspondence for interactions between quantum and gravitational fields. Furthermore we cover simulations of a quantum field in a FRW metric and compare them with simulations of a classical field in the same metric. This shows that the Classical-Quantum Correspondence is a good technique to combine quantum fields with classical gravity, and get the full evolution of both without the need to do the same equation itteratively.Show less
