Non-decoupling of heavy scalars in cosmology

The theory describing physics at the highest energy scales likely contains extra dimensions, whose internal degrees of freedom result in many massive field and particles. At accelerator experiments these fields and particles generally decouple from the low energy physics. However, in cosmology gravity couples everything, thereby invalidating the decoupling assumption. In this thesis we have shown that massive particles and field that do not decouple during cosmological inflation will generate corrections, which lead to possibly observable features in the Cosmic Microwave Background. Furthermore, in specific setups where the massive particles and fields do decouple their stability can still be affected by the low energy physics energy scaleNWO Veni and NWO VICIUBL - phd migration 201