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Title: Theoretical and observational constraints on brane inflation and study of scalar perturbations through the effective field theory formalism
Author: Sypsas, Spyridon
ISNI:       0000 0004 5357 3996
Awarding Body: King's College London (University of London)
Current Institution: King's College London (University of London)
Date of Award: 2014
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In this thesis, we study observational signatures of cosmic (super)strings in the context of D brane inflation and properties of scalar inflaton perturbations on generic homogeneous inflating backgrounds. In the first part, we study the properties of cosmic superstrings produced at the end of inflation in two widely used effective models within a string theory framework, namely the D3/D7 and D3/¯D 3 models. For the D3/D7 model, we show that the symmetry breaking during the waterfall stage is anomalous and cancellation of this anomaly in combination with the moduli stabilisation procedure results in local axionic strings. In addition, we argue that the model is inconsistent with supergravity constraints on constant Fayet Iliopoulos terms. Moreover, we study radiative processes of cosmic superstrings on warped backgrounds. We argue that contrary to previous results in the literature, placing the string formation in a natural context such as D3/¯D 3 inflation, restricts the forms of possible radiation from these objects. Motivated by these string models, which inevitably result in the presence of heavy moduli fields during inflation, in the second part, we construct an effective field theory that captures the effects of massive scalars on the low energy dynamics of inflaton perturbations. We compute the energy scales that define the validity window of the Effective Field Theory (EFT) such as the scale where ultra violet (UV) degrees of freedom become operational and the scale where the EFT becomes strongly coupled. We show that the low energy operators related to heavy fields lift the strong coupling scale of the theory and result in a non linear dispersion relation for the light modes. Assuming that these modes cross the Hubble scale within the dispersive regime, we compute several observables and show how they are directly related with the scale of UV physics.
Supervisor: Sakellariadou, Maria Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available