Physics Division, MS 50R5032
These are privileged times to be a cosmologist. Recent years have witnessed unprecedented progress in observational and computational techniques and we are now able to quantify cosmological properties with unprecedented accuracy. My work builds upon this observational accuracy by establishing a connection with viable models and providing an interface between theory and observation. I'm interested in the development of techniques that take into account numerous theoretical issues in the analysis of data and placing constraints on phenomenological models that are favoured by the observations. My interests span from the Early to the Late Universe, with a side interest on Quantum Gravity that I attempt to indulge as often as possible. I focus on early time inflation and late time acceleration - dubbed dark energy.
I focus on the dynamics of inflationary models particularly single- field slow-roll and have studied and improved upon the existing inflationary signature - known as 'consistency equation' - that may one day provide us with a smoking gun for the inflationary paradigm should we ever come to detect gravitational waves. Nonetheless, the knowledge of the full implications of this peculiar relation between the two primordial spectra of scalar and tensor perturbations, needs to be taken into account when projecting analyses of observational data so as to allow for fully consistent theory predictions.
I am also interested in the obtaining and improvement of the observational constraints we are able to place on these models based on both WMAP the upcoming PLANCK satellite's observations of the CMB. As the accuracy of data continues to increase, new features of the underlying inflationary potential will potentially become observable and i have obtained a new technique that allows for a considerable reduction on the uncertainty on derived inflationary and other cosmological parameters, based on obtaining constraints at the cosmological scale that maximizes the decorrelation between cosmological parameters.
Observational studies of DE present a serious challenge for data analysis. Since we lack an underlying fundamental theory, we have at present no well-defined framework within which to develop and project such analyses. Conversely, the data does not allow for discrimination between competing theoretical models and in fitting data, one is therefore faced with the two-fold challenge of accommodating fundamental theory as well as ensuring that the analysis remains tractable regarding the number of free parameters to be constrained by the dataset.
In light of this, I am interested in features of DE parametrizations that allow for theoretically motivated arguments while meeting observational limitations. Specifically this involves looking for features that allow for a wider range of dynamics, while at the same time minimizing the degeneracies likely to arise in each parametrization when considering other unknowns such as the remaining set of cosmological parameters to take in the analysis.
With this in mind I have examined the bias induced in the reconstructed dark energy equation of state, when there is a bias on e.g. the cosmic curvature or dark matter content, and have shown that even given perfect Hubble, distance, and volume measurements - and even in the case of a parametric free EoS - the resulting bias on w will be up to two orders of magnitude larger than the corresponding error in the curvature or matter
Apart from this I am also interested in the implications that an early dark energy component may have for dynamics and other signatures at low redshift. I have investigated the link between the presence of dark energy at an early time - focusing on the well known bounds imposed by Big Bang Nucleosynthesis and the surface of last scattering - and concluded these place stringent bounds on the range of models allowed by observations, particularly if we are interested in matching those with a non minimally coupled scaling field (quintessence models).
In this direction and exploring the link with cosmology i have attempted to develop a framework for investigating the spectrum of primordial perturbations generated in a phase where the intermediate, semi-classical regime of Loop Quantum Cosmology applies.
This regime is a symmetry reduction to isotropic backgrounds which basically translates in an intermediate region between the fully quantum treatment and the classical approximation, and where spacetime can be treated as a continuum but nonperturbative quantum effects modify the standard cosmological evolution.
I considered an inflationary era driven by a canonical scalar field and occurring in the semiclassical regime, and investigated the amplitude of the primordial density perturbation spectrum generated under this framework.
I found that the scalar spectrum can be blue-tilted and far from scale invariance, and tuning of the quantization ambiguities - which otherwise involve parameters generally not constrained by the theory - is necessary for agreement with measurements of the scalar spectral tilt and tensor to scalar ratio. The quantizing of the matter field at sub-horizon scales can despite this provide a check of such quantization schemes and the consistency with observations.