Bachelor Thesis With Prof. Mertsch in 2020

 

Gamma-rays from the Galactic Centre

Context:
If dark matter has appreciable interactions with ordinary matter, it can produce additional radiation, especially in regions of high dark matter density like the Galactic centre. Intriguingly, an excess of high-energy gamma-rays from the Galactic Centre has been observed, but it is currently unclear whether this is due to dark matter or due to astrophysical sources like millisecond pulsars.

Goals:
You will model the diffuse emission of gamma-rays from the inner Galaxy which is dominantly due to the interaction of high-energy cosmic rays with hydrogen gas. You will use actual radio surveys of gas in the Milky Way to say where along the line of sight the radiation is produced.

Requirements:
An interest in the dark matter problem and willingness to learn some new numerical methods.

Dark cosmic rays

Context:
In several theories beyond the Standard Model of particle physics, dark matter can possess a (tiny) electrical charge. These particles would be subject to acceleration and transport processes similar to ordinary cosmic rays. A flux of such "dark cosmic rays" can potentially be detected in current direct detection and neutrino experiments.

Goals:
You will learn about cosmic ray acceleration and transport processes before investigating the
extension to the case of millicharged dark matter particles. You will compute the expected flux
of dark cosmic rays at Earth and identify the regions of the dark matter parameter space that can
be probed.

Requirements:
An interest in the dark matter puzzle and in cosmic ray physics, good analytical skills.

Anisotropic cosmic ray diffusion and its impact on the gamma-ray sky

Context:
The transport of cosmic rays is dominantly a diffusion process. Models that assume this diffusion to be isotropic cannot reproduce remote observations, for example via the observation of high-energy gamma-rays. Theoretically, it is known, however, that relativistic charged particles diffuse predominantly along the galactic magnetic field. While it might be challenging to model this numerically, it can have profound consequences on the diffuse gamma-ray emission across the Galactic plane.

Goals:
You will refine an existing numerical code that models the anisotropic diffusion of cosmic ray protons in three dimensions. You will then compute the expected diffuse gamma-ray emission from these protons and compare it with observations.

Requirements:
An interest in cosmic ray physics and a taste for numerical work. Good coding skills (in C++ and Python) are required.

The ionisation puzzle

Context:
Cosmic rays are the prime agent of ionisation in dense environments that cannot be penetrated by electromagnetic interaction. This ionisation is crucial for interstellar chemistry and for the "ecology" of the Galaxy. Yet, there is a large discrepancy between what is observed from molecular clouds and what is expected from cosmic rays. It has been suggested that this could be due to large fluctuations as a function of position.

Goals:
You will develop a quantitative model for predicting the expected fluctuations in the ionisation rate. In the end, you will be able to tell whether this is a viable explanation for the discrepancy.

Requirements:
An interest to learn about cosmic rays. Both analytical and numerical approaches are possible in
principle.