Related papers: Observable gravitational waves in pre-big bang cos…
While the observed nearly scale-invariant initial power spectrum is regarded as one of the favorable evidence of the standard inflationary cosmology, precision observations of the Cosmic Microwave Background (CMB) anisotropies also suggest…
Recent Planck measurements show some CMB anomalies on large angular scales, which confirms the early observations by WMAP. We show that an inflationary model, in which before the slow-roll inflation the Universe is in a superinflationary…
I report recent studies on the evolution of perturbations in the context of the ``pre-big-bang" scenario typical of string cosmology, with emphasis on the formation of a stochastic background of relic photons and gravitons, and its possible…
The advent of gravitational-wave (GW) astronomy has presented us with a completely new means for observing the Universe, allowing us to probe its structure and evolution like never before. In this thesis, we explore three distinct but…
We examine the effect of spatial curvature in the pre-big-bang inflationary model suggested by string theory. We study $O(\alpha ')$ corrections and we show that, independently of the initial curvature, they lead to a phase of exponential…
The B-mode polarization of the cosmic microwave background (CMB) provides a unique window into tensor perturbations from inflationary gravitational waves. Survey effects complicate the estimation and description of the power spectrum on the…
While large scale cosmic microwave background (CMB) anisotropies involve a combination of the scalar and tensor fluctuations, the scalar amplitude can be independently determined through the CMB-galaxy cross-correlation. Using recently…
To efficiently probe primordial non-Gaussianity using Cosmic Microwave Background (CMB) data, we require theoretical predictions that are factorizable, \textit{i.e.}\ those whose kinematic dependence can be separated. This property does not…
We examine the constraints cosmological observations can place on any trans-Planckian corrections to the primordial spectrum of perturbations underlying the anisotropies in the Cosmic Microwave Background. We focus on models of…
We review current observational constraints on the polarization of the Cosmic Microwave Background (CMB), with a particular emphasis on detecting the signature of primordial gravitational waves. We present an analytic solution to the…
This paper is the third in a series of theorems which state how cosmological observations can provide evidence for an early phase of acceleration in the universe. Previous theorems demonstrated that the observed power spectrum for scalar…
Recent work by Ringermacher and Mead has revealed discrete oscillations in the cosmological scale factor, suggesting that spacetime may exhibit vibrational properties akin to those of a crystal. Building on this idea, we propose a novel…
The leading candidate for the very early universe is described by a period of rapid expansion known as inflation. While the standard paradigm invokes a single slow-rolling field, many different models may be constructed which fit the…
The latest Planck results show a power deficit in the temperature anisotropies near $\ell \approx 20$ in the cosmic microwave background (CMB). This observation can hardly be explained within the standard inflationary…
We briefly summarize the impact of the recent Planck measurements for string inflationary models, and outline what might be expected to be learned in the near future from the expected improvement in sensitivity to the primordial…
A thermal gravitational wave background can be produced in the early Universe if a radiation dominated epoch precedes the usual inflationary stage. This background provides a unique way to study the initial state of the Universe. We discuss…
Observations of the Cosmic Microwave Background (CMB) have cemented the notion that the large-scale Universe is both statistically homogeneous and isotropic. But is it invariant also under reflections? To probe this we require…
The standard $\Lambda$CDM cosmological model informed by cosmic microwave background (CMB) anisotropies makes a precise prediction for the growth of matter density fluctuations over cosmic time on linear scales. A variety of cosmological…
The generation of large-scale magnetic fields in inflationary cosmology is explored, in particular, in a kind of moduli inflation motivated by racetrack inflation in the context of the Type IIB string theory. In this model, the conformal…
As cosmology rapidly approaches the data-dominated phase of stage IV large scale structure surveys, the modelling of nonlinear scales has become a serious challenge that faces the community, particularly when analysing models beyond $w$CDM.…