This work investigates gravitational wave production in the early universe and identifies potentially observable features, thereby paving the way for future gravitational wave experiments. It focuses on gravitational wave production in two scenarios: inflation in a model inspired by loop quantum gravity, and preheating at the end of inflation. In the first part, it is demonstrated that gravitational waves' spectrum differs from the result obtained using ordinary general relativity, with potentially observable consequences that could yield insights into quantum gravity. In the second part, it is shown that the cosmic gravitational wave background is anisotropic at a level that could be detected by future experiments. Gravitational waves promise to be an rich source of information on the early universe. To them, the universe has been transparent from its earliest moments, so they can give us an unobstructed view of the Big Bang and a means to probe the fundamental laws of nature at very high energies.

Nominated as an outstanding Ph.D. thesis by Imperial College London Includes a thorough introduction covering all topics needed to understand this research field Provides detailed explanations of how the new calculations were performed Describes in detail the implementation of the numerical simulations Includes supplementary material: sn.pub/extras

Inhalt
Introduction.- Chiral Tensor Power Spectrum from Quantum Gravity.- Anisotropic Gravitational Wave Background from Massless Pre-heating.- Concluding Remarks.- Appendix.