# Bachelor thesis with Prof. Lesgourgues/Prof. Mertsch in 2017

**For the summer semester 2017, Prof. Lesgourgues, Prof. Mertsch and their research group propose six topics related to cosmology and astroparticle physics. Since Prof. Lesgourgues and his postdocs do not speak fluent german yet, most of the interactions between students and supervisors will be in English.**

A better likelihood algorithm for the galaxy survey of the EUCLID satellite

**Supervisor:** Julien Lesgourgues (and Maria Archidiacono, Sebastien Clesse)

**Context:**

The EUCLID satellite will be launched by ESA in 2020 and will map galaxies in the universe with unprecendented precision, in order to learn more about the properties of our universe. Our group is preparing the comparison between theoretical models and the future data set. In particular, we develop several numerical tools related to EUCLID, including a piece of code containing the likelihood function modelling this data set. For the moment, we use such tools on ``mock data sets'' (randomly generated data sets) for checking and validation. In a few years they will be used on the real data set.

**Goal:**

One of the likelihood codes that we are developping is slow. Very recently (in January 2017), a few researchers published a paper showing that the problem can be formulated mathematically in a different way, which leads to much faster calculations. The goal is to study this method analytically, and then to implement it in our numerical tools.

**Requirements:**

The student should be motivated enough in order to learn some advanced formalism describing the theoretical modelling of astronomical and cosmological data sets. She/He should have some reasonnable knowledge of both C and C++, in order to achieved the coding part.

Simulations of Black Holes as components of Dark Matter

**Supervisor:** Sebastien Clesse

**Context:**

It is possible that Dark Matter, accounting for about 30% of the energy content of the Universe today, could be made of massive primordial black holes (larger than a stellar mass), formed in the early Universe and that could be hidden today in faint dwarf galaxies. This idea recently recieved a renewed interest, because it could be an explanation of the events detected last year by the gravitational wave interferometer aLIGO.

**Goal:**

The goal of this project is to develop simple N-body simulations to study the evolution of black hole clusters, accounting for the Newtonian force between them at short distances. For this purpose two codes could be used and compared: a simplified code already developed last year by a previous bachelor student, and a more precise code developed in the general context of studying dark matter clustering (the gadget code), that would need to be slightly modified for our pruposes.

**Requirements:**

This project requires a clear taste for numerical simulations (especially, some enthusiasm, because the difficulty of the coding is not so high). Some familiarity with C and C++ would be a plus.

Testing the neutrino mass hierarchy with cosmology

**Supervisor:** Maria Archidiacono (and Julien Lesgourgues)

**Context:**

The Euclid satellite by the European Space Agency will be launched in 2020 and will survey the local Universe, providing extremely accurate measurements of cosmological observables, which are sensitive to neutrinos. Indeed, forecasts show that the neutrino mass sum will be constrained by Euclid with the best accuracy ever. However it is still under debate whether such an accuracy will be enough to single out the ordering between each of the three individual neutrino masses. This project is aimed at checking whether cosmology, in particular Euclid, would be able to pin down the neutrino mass hierarchy within the next few years, before ground-based experiments such as ORCA and PINGU.

**Goals:**

The student will learn the basic concepts about the impact of massive neutrinos on cosmological observables. He/She will compute theoretical predictions of Cosmic Microwave Background temperature anisotropies and of galaxy power spectrum in massive neutrino cosmologies. Finally he/she will forecast the sensitivity of Euclid to the neutrino mass ordering.

**Requirements:**

Some basic knowledge of C (in order to use and modify the CLASS code) and Python (in order to use and modify the MontePython code).

Acceleration of cosmic rays at galactic wind termination shocks

**Supervisor:** Philipp Mertsch

**Context:**

The earth is constantly bombarded by a flux of charged particle from outer space, called cosmic rays, some with energies up to 10^{20} eV. Most cosmic rays are thought to be accelerated by the blast waves left behind by supernova explosions. However, at the highest energies these sources cannot reach the required energies. Instead, giant shock waves surrounding our Galaxy could be the site of acceleration to extremely high energies.

**Goals:**

In this project you will analytically or numerically compute the spectrum of cosmic rays accelerated at galactic wind

termination shocks and find ways of testing the model by comparing with observations.

**Requirements:**

Familiarity with solving basic partial differential equations and an interest to learn about high-energy astrophysics!

Search for lines in the FERMI gamma-ray data

**Supervisor:** Alessandro Cuoco

**Context:**

The FERMI sattelite, operational since several years, is a gamma-ray telescope, observing high-energy photons propagating in the universe. Most of these photons are expected to come from astrophysical sources, and to be produced by various mechanism involving only the standard model of particle physics. However, the observation of unexpected emission lines in the data could in principle arise from Dark Matter annihilation, and tell us about the properties of Dark Matter. Alessandro Cuoco works as a theorist on the analysis and interpretation of the FERMI data.

**Requirements:**

The student will use different softwares and codes written in different languages; no strong coding skills needed, but some familiarity (and taste for) compter-based work in general.

Dark Matter constraints from AMS02 cosmic-ray antiprotons

**Supervisor:** Alessandro Cuoco

**Context:**

The AMS detector, located on the International Space Station, measures theflux of several particles propagating in the cosmos, including anti-protons. Researchers are trying to interpret the anti-proton spectrum in terms of astrophysical phenomena, plus eventually signatures from Dark matter annihilation (this activity could lead to „indirect dark matter detection“).

**Goals:**

Last year, a previous bachelor student has worked on this, and has obtained interesting results. This year, the student should start from that point, and rewrite the code written by the previous student in a much more efficient way, to make it faster. Then, a more ambitious analysis could be performed, involving more data, models and assumptions.

**Requirements:**

This project definitely requires good coding skills. The student should at the same time be interested in the underlying physics, and find it useful and fun to do some numerical optimisation, and then to launch big runs on the RWTH computing cluster.