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Formal aspects of cosmological models: higher derivatives and non-linear realisations

PhD ceremony:R. Klein, PhD
When:December 13, 2018
Supervisors:prof. dr. D. (Diederik) Roest, prof. dr. E.A. (Eric A) Bergshoeff
Where:Academy building RUG
Faculty:Science and Engineering

The field of cosmology deals with the properties and evolution of the universe as a whole, and tries to answer questions such as 'What did the universe look like in the past?', 'How did it evolve into its current state?' and 'What will it look like in the future?'.

In this thesis we investigated several formal aspects of cosmological models that are intended to describe the accelerated expansion of the very early universe (also called inflation) and that of the current universe.

Firstly we have examined under which conditions one can avoid particular unwanted instabilities that often appear in models with so-called higher derivatives. Our findings led us to introduce a classification of models that are free of such instabilities.

We have also investigated particular mathematical properties of so-called non-linear realisations of space-time symmetries. Such non-linear realisations occur naturally whenever space-time symmetries of a model get spontaneously broken. Lastly, based on particular broken space-time symmetries, we have introduced new inflationary models that can be tested in the near future with the newest generation of satellite experiments.