Bachelor Thesis With Prof. Mertsch in 2021

 

Millicharged dark matter and plasma instabilities

Context:
80% of the matter in the Universe is in the exotic form of dark matter (DM) which so far we know relatively little about. While there are constraints on its electric charge, in a certain class of models DM has a small fractional charge. The phenomenology of this millicharged DM is rather rich and many of the effects known from ordinary astrophysical plasmas can operate here, too, and can be searched for.

Goals:
After becoming acquainted with the basics of millicharged DM, you will derive the dispersion relation for the various plasma wave modes it can sustain. We will look for the unstable, growing modes and think about what astrophysical observations could be used to test those.

Requirements:
An interest in the dark matter puzzle and good analytical skills.

Stochastic fluctuations of low-energy cosmic rays

Context:
Low-energy cosmic rays are believed to be the main source of ionization in star-forming regions. The observed and predicted ionization rates are, however, different by orders of magnitude which might be due to fluctuations in cosmic-ray density at different positions in our Galaxy. More importantly, the predicted fluctuations for standard candidate sources like supernova remnants do not seem to sufficiently resolve the problem. It has been suggested that the contribution from different classes of sources, e.g. stars or pulsars, to the intensities of low-energy cosmic rays might also be important for the fluctuations.

Goals:
You will extend the current model to predict the fluctuations for different classes of cosmic-ray sources, e.g. stars or pulsars. You will then predict the corresponding fluctuations of the ionization rate to compare with data.

Requirements:
An interest in cosmic rays and a taste for numerical work.

Nonlinear cosmic-ray transport in the vicinity of supernova remnants

Context:
According to the standard paradigm, cosmic rays are accelerated at supernova remnant shocks and then released into the interstellar medium. The escape of these particles from the shocks is, however, still an open issue, especially in the energy range below a few GeV. This is because cosmic rays themselves, as they propagate, generate magnetic turbulence which in turn controls their transport. Such a phenomenon can be addressed numerically by solving a set of non-linear differential equations and the result might have a profound consequence in predicting the intensities of low-energy cosmic rays in our Galaxy.

Goals:
You will develop a numerical code for solving the coupled differential equations. You will then apply it to some systems of interest like supernova remnants W28, W44, and IC443 to predict physical quantities of interest.

Requirements:
An interest in cosmic rays and numerical methods for solving differential equations.

A 3D map of the Galaxy

Context:
The study of the structure of the Milky Way is impeded by our vantage point inside the Galactic disk. Thanks to Galactic rotation, however, we can use the Doppler shift of emission lines to deproject the data from surveys of Galactic atomic and molecular gas. Such 3D maps are urgently needed for searches of signals from dark matter and for a better understanding of star formation and the evolution of galaxies.

Goals:
You will familiarise yourself with variational inference, a set of techniques from the Bayesian toolbox, that allows for a systematic deprojection. Building on an existing code, you will apply such an algorithm to the measurements of the 21cm hydrogen line from a recent all-sky survey. The final result will be a 3D map of the atomic hydrogen in the Galaxy, together with an estimate of its uncertainty, possibly propagated to constraints from dark matter searches.

Requirements:
An interest in Galactic astrophysics and a taste for numerical work.