This thesis is dedicated to the exploration of the primordial dark ages: unknown physics during the earliest stages of the Universe’s expansion that have not yet been directly probed by... Show moreThis thesis is dedicated to the exploration of the primordial dark ages: unknown physics during the earliest stages of the Universe’s expansion that have not yet been directly probed by observations. Cosmic inflation is a burst of exponential expansion of space after the “Big Bang”. The energy that drives inflation must be transferred to elementary particles and radiation. This process is called reheating. The unknown expansion history of the universe during the reheating era connects the cosmic microwave background (CMB) observations to inflationary physics. CMB is a relic radiation that provides us a snapshot of the primordial universe. Both the inflationary and reheating eras generate signatures to be seen via upcoming gravitational waves and CMB polarization experiments. In this thesis we show analytically a scaling behaviour that allows for an easy estimate of the reheating efficiency for one broad family of multi-field models of inflation that is called α-attractors. We show the influence of the asymmetry around the minimum of potential on the reheating efficiency. Moreover, we study the predictions for chiral gravitational waves production by a spectator gauge field sector in scalar single-field inflation. Finally, we present a new class of inflationary models that is called “shift-symmetric orbital inflation”. Show less
This thesis contributes to studying primordial cosmology theories and their detectability in future observations. The first part of the thesis studies a class of inflation models with curved field... Show moreThis thesis contributes to studying primordial cosmology theories and their detectability in future observations. The first part of the thesis studies a class of inflation models with curved field spaces, which are typically motivated in high energy physics theories. The second part of the thesis focuses on one particularly important cosmological observable -- primordial non-Gaussianity, whose phenomenology may reveal new physics effects in the very early Universe. Show less
In this thesis we study the landscape of gravitational models which modify GR by introducing an additional scalar degree of freedom (d.o.f.) to source Cosmic Acceleration. In particular we... Show moreIn this thesis we study the landscape of gravitational models which modify GR by introducing an additional scalar degree of freedom (d.o.f.) to source Cosmic Acceleration. In particular we answer the question "What is the complete set of theoretical conditions a gravitational model must satisfy, in order to give a theoretically viable cosmology?". In order to study the theoretical stability of extended models of gravity we emplout the E ective Field Theory of Dark Energy and Modied Gravity (EFToDE/MG). This is a unifying framework which allows us to study the landscape of gravitational models in a broad and model independent way. This will allow us to answer the research question in a model independent way. Show less
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... Show moreThe 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 scale Show less
