Master Projects in Astroparticle Physics and Cosmology (2017-2018)

 

The group of Cosmology proposes 6 Masterarbeit topics , but expects to select only 4 students. These projects are meant to start in the next winter semester (mid-October 2017). However, some of them could also be started in September if the student prefers. The projects will be given in priority to RWTH students who followed the courses "Relativity and Cosmology" and "The Perturbed Universe". There will be a meeting of information about these projects on Tuesday 18.07 at 15:00, during the end of the "Perturbed Universe" exercise session.

These projects will be supervised Pr. Julien Lesgourgues and the two post-docs of the group:

Maria Archidiacono (archi@phys.au.dk)
Christian Fidler (fidlerc@me.com)

The PhD students will also help the students whenever possible.

Project 1: New methods in relativistic N-body simulations

Field: Cosmology (Large Scale Structure)
Main supervisor: Christian Fidler
Other supervisor: Julien Lesgourgues
Numerical aspects: significant amount of coding, mainly in C/C++

Abstract:
In the recent years significant progress has been made in the field of relativistic N-body simulations; describing the non-linear evolution of structures during matter and Lambda domination in terms of Einsteins equations instead of the Newtonian theory. In particular the semi-analytical framework of Newtonian motion gauges allows a translation between a Newtonian and a relativistic simulation. It is numerically efficient and can be applied to a large range of potential cosmologies. The student will learn the methodology, develop Newtonian motion gauges for realistic cosmologies and simulate the properties of their space-time employing the CLASS code. The project aims to provide accurate numerical forecasts for ESA’s Euclid satellite mission, and explore the impact of the various components of our Universe on the cosmic evolution.

Project 2: Non-linear correction and baryonic feedback in high-precision galaxy surveys

Fields: Cosmology (Large Scale Structure)
Main supervisor: Maria Archidiacono
Other supervisor: Julien Lesgourgues, Thejs BrinckmannJulien Lesgourgues
Numerical aspects: data manipulation and significant amount of programming, mainly in C and Python

Abstract:
In the near future, the European Space Agency satellite Euclid will map the galaxies in our local Universe with the best precision ever. The measurements will extend down to very small scales, where linear perturbation theory breaks down and the clustering becomes non-linear. Therefore, in order to fully exploit future data, it will be crucial to have an accurate prediction of non-linear effects, possibly including the low-redshift baryonic feedback (e.g. SuperNovae and stellar winds). In this project, the student will implement a method developed recently for estimating non-linear corrections in the CLASS code. The outcome will allow to test the impact of the non-linear effects on the determination of the neutrino mass from Euclid.

Project 3: Theory of Large Scale Structure in presence of massive neutrinos

Field: Cosmology (Large Scale Structure)
Main supervisor: Christian Fidler
Other supervisor: Julien Lesgourgues, Maria Archidiacono
Numerical aspects: the project is mostly analytical

Abstract:
The formation of structure in a pure dark matter Universe has been explored in great detail, both numerically and analytically. One important additional ingredient, not based on speculative physics, are massive neutrinos. These move at velocities close to the speed of light early on, while they eventually slow down and are captured by the forming dark matter clusters. The student will learn the methodology employed in the field of large scale structure and work in the development of new models, describing the impact of neutrinos on the formation of galaxies and halos. The project is important for the analysis of future surveys, such as ESA’s Euclid satellite mission, since the gravitational impact of the Neutrinos introduces a bias between the observable objects (galaxies and halos) and the underlying dark matter distribution. Another related topic is the impact of the neutrinos on the redshift-space distortions affecting our observations.

Project 4: Higher Performance Computing with CLASS

Field: Numerical Cosmology
Main supervisor: Julien Lesgourgues
Other supervisor: Christian Fidler, Deanna Hooper
Numerical aspects: suited for students passionate of high performance computing, numerical methods, parallelisation/vectorisation tools, etc.

Abstract:
The Aachen group leads the development of a large and complex public code, CLASS, used worldwide for calculating CMB and Large Scale Structure observables. This code uses parallelisation, and its speed scales almost linearly up to 8 cores. The level of parallelisation needs to be improved in order to get better performance on the most modern CPUs (Intel Xeon up to 64 cores, MIC/Xeon Phi up to ~240 cores). We also want to improve the performances of the code by using a better vectorisation of the operations, and by off-loading some calculations on GPUs (graphical processors). This will be partly possible by adding appropriate commands into the code, but sometimes it will be necessary to revisit completely the choice of numerical methods used in different parts of the code. This project could almost be done by a student in the IT department. However it sounds better to do it with a physics student who will be guided by his/her physical intuition, and more likely to find relevant approximations. The project is also suited for physics students for other reasons ways: first, the student will need to improve his knowledge of cosmology in order to understand the code; this is important in order to make good coding choices! Second, once the code performs very well, we can tackle a few problems that were not treated before because the code was too slow; this will lead to a couple of publications in cosmology/astrophysics. Reserved to big fans of numerics!

Project 5: Imprints of reionisation in the Cosmic Microwave Background

Field: Cosmology (CMB physics)
Main supervisor: Christian Fidler
Other supervisor: Julien Lesgourgues
Numerical aspects: significant amount of coding, mainly in C/C++

Abstract:
The age of reionisation starts when the first stars are born and their light reionises the intergalactic medium. While the early Universe is constrained by the Cosmic Microwave Background and the late Universe by the large scale structure, the age of reionisation is almost unexplored. Potentially observable signatures of the Universe during this epoch are thus of great interest. The leading impact of reionisation on the microwave background is an almost uniform suppression due to collisions of photons with the intergalactic medium, providing a 10% optical depth for reionisation. Beyond this effect, the collisions at reionisation imprint a rich but very faint structure in the microwave background, which resembles the ionisation history and the distribution of the intergalactic medium at reionisation. The goal is to define potential observables (B-mode polarisation, Non-Gaussianity), develop the tools needed for a numerical simulation, and produce forecasts for current and future surveys.

Project 6: Defining an imaginative and interactive smartphone application and/or website for cosmology outreach

Field: Cosmology, Outreach and Numerics
Main supervisor: Julien Lesgourgues
Other supervisors: Deanna Hooper (PhD student) and others
Numerical aspects: requires excellent programming skills, including HTML, java, python, skills with graphical interfaces...

Abstract:
This is a very unconventional project, with a lot of freedom, and requiring much imagination and creativity. What would you do if you wanted to create a website and/or a smartphone application aimed at stimulating the interest of a very large audience for cosmology, and in particular CMB physics? Could you invent interactive simulations, graphical animations, pedagogical applications, and code them in an attractive and professional way? You will participate to brainstormings with several members of the Aachen cosmology group, in order to define several ideas, and will try to implement some of them concretely. There is already a platform of codes and graphical interfaces developed by some of us. We only need more time, imagination and manpower to turn this into a beautiful project! This topic is unusual for a master project in physics, but it sounds perfectly appropriate, since you will need to improve a lot your level in cosmology (as much as if you were doing traditional research). Choose this only if you are an enthusiastic person, if you like to explain physics to people, and if you have very good coding skills (previous experience with web mastering and/or writing smartphone apps would be a plus).