Theory meets data: modelling non-linear scales for dark energy experiments

Research Group: 
Astronomy Unit
Number of Students: 
Length of Study in Years: 
Full-time Project: 
QM Scholarship
Project Description: 
During the last few years, we have entered the “golden era” of observational cosmology. The standard cosmological model fits the data extremely well, but requires the existence of two exotic constituents, namely dark energy in the form of a cosmological constant, and cold dark matter. Dark energy currently dominates the Universe and it is responsible for its accelerated expansion.

Our ignorance about the nature of dark energy is arguably the most important issue in cosmology today. Theoretical cosmologists have suggested that dark energy could be a dynamically evolving scalar field, or it could be a manifestation of the laws of gravity changing on large, cosmological scales. It can also be the case that dark energy and dark matter interact with each other non-gravitationally, e.g. by decaying into one another!

In the next few years, state-of-the-art cosmological surveys with instruments like the Dark Energy Spectroscopic Instrument (DESI), the Euclid satellite, and the Square Kilometre Array (SKA), are promising to map the large scale structure of the Universe and pin down the nature of dark energy.

The Astronomy Unit at Queen Mary University of London has access to Euclid and the SKA. The student will gain experience in theoretical and observational cosmology, dark energy theory, numerical methods, and will be part of a vibrant international community of scientists.

This PhD project aims to tackle one of the biggest challenges in theoretical and observational cosmology: how to model accurately and efficiently the non-linear (that is, small scale) behaviour of dark energy models. Until recently, we did not need to worry too much about having accurate theoretical templates to fit to data, since the small scale, non-linear information was not accessible by experiments. In the next few years, however, these small scales are going to be measured with unprecedented precision, and unless we can trust our theoretical modelling tools we will have to throw all this extra information away!

The student will learn about models of dark energy and about various approaches that have been used to model non-linear scales, for example the SPT (Standard Perturbation Theory) methods. Then the student will study more sophisticated approaches like EFTofLSS (Effective Field Theory of Large Scale Structure). We already know the SPT range of validity, and we have a good idea on the improvements made by using EFTofLSS. The student will make a comprehensive comparison between the two methods and forecast their ability to improve the constraining power of future surveys like Euclid and the SKA. The student will investigate the performance of the two methods for the standard cosmological model as well as for non-standard models, with special emphasis on those where dark energy and dark matter are allowed to interact.

A degree in Physics, Mathematics, or similar.
Some programming experience (e.g. Python or C/C++) is desirable.

SPA Academics: 
Alkistis Pourtsidou