Cosmological aspects of unified theories
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Λυμπέρης, Ανδρέας
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Abstract
In this thesis, we study cosmological aspects of some well-known dark energy models, and
extending our investigation into Unified Theories. We explore the existence of geodesically
complete singularities in quintessence and scalar-tensor quintessence models using analytical
expressions for the scale factor and the scalar field. Next, using the Tsallis entropy
and applying the first law of thermodynamics we construct several cosmological scenarios.
The sequence of dark energy span and, depending on the value of the parameter of dark
energy equation of state, during the evolution, experience the phantom-divide crossing
and can be quintessence or phantom-like. Finally, we revisit inflation with non-canonical
scalar fields by applying deformed steepness exponential potentials. A significant advantage
of this approach is that free parameters, such as the non-canonicality exponent do
not need to acquire unnatural values. The resulting scenario can lead to inflationary observables in remarkable agreement with observations.
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Keywords
Modified gravity, Unified theories, Dark energy, Cosmological confrontation