Probing the early Universe with cosmic large-scale structure
Contact Person : Prof. Jaan Einasto (einasto@aai.ee)

Our theoretical understanding of the formation and evolution of cosmic large-scale struc- ture (LSS) has proven to be a powerful tool (along with cosmic microwave background (CMB) experiments and type Ia supernova surveys) in helping to establish “concordance cosmological model” – the standard model of cosmology. On one hand the standard cos- mological model is remarkably simple: in its most basic form a model with only 5-6 free parameters is able to accommodate a large body of diverse observational data. On the other hand we should be worried since we have good physical theories available for only ∼ 5% of the stuff out there, while the rest ∼ 95% is provided by poorly understood dark components – dark energy (DE) and dark matter (DM). Mostly from CMB mea- surements we have been able to learn a great deal about the initial fluctuations: we know that the initial fluctuations are compatible with the predictions of the simplest inflationary models, i.e. Gaussian adiabatic perturbations with approximately scale- free Harrison-Zeldovich spectrum. Any detectable deviation from Gaussianity would certainly be extremely interesting as it would tell us something about the nature of the physical processes setting up these primordial perturbations. So far the strongest upper bounds (there has been no convincing detection so far) on allowed level of non- Gaussianities has been obtained from CMB measurements. However, it has been shown that future LSS surveys will be at least as competitive as upcoming CMB experiments in constraining the possible level of primordial non-Gaussianity. Indeed, from the anal- ysis of the current LSS data there are already some hints that might argue in favor of non-Gaussian models:
• unexpectedly massive galaxy clusters at high redshifts;
• surprisingly large number of very rich superclusters;
• excess power on the largest scales as hinted by several recent power spectrum measurements from the Sloan Digital Sky Survey (SDSS) galaxy data.
In this PhD project the student will work on available LSS datasets, particularly with the data from the SDSS. The main focus of the study will be:
• search for primordial non-Gaussianities; • constraining the properties of dark components (DE, DM) throughout cosmic evo-
lution.
As the statistical analysis (in particular, testing of statistical methods and error analy- sis) of the LSS data often requires comparison with simulation outputs, the student will most probably run some cosmological N-body simulations or use already available sim- ulation data. These tasks will understandably require some knowledge of programming languages, and thus it would be beneficial if the student has already some experience with computer programming.