Andrew Eberhardt: Galactic structure resulting from ultra light dark matter

This summer I worked with the astrophysics department at the University of G ̈ottingen with Jens Niemeyer. We worked on developing a better understanding of how the scalar field dark matter model effects small scale structure. Specifically, we looked at the effect of a multi species model on stellar heating constraints using numerical simulations of a galactic halo.

I was able to make a number of contributions to the group I was working with during my stay. First and foremost, I was able to share previous results simulating classical and quantum fields in the context of astrophysical systems. This involved both estimations of the manner in which quantum corrections could effect early universe simulations of structure growth, but also useful in understanding the potential effect of multiple species dark matter models. I had studied both of these effects in the course of my thesis research and was able to give insight on a number of projects that they had in progress. With respect to better understanding multi field dark ultra light dark matter models I worked out a calculation for how this model would effect existing stellar heating bounds on scalar field dark matter, see figure 1.

Figure 1: Constraints due to stellar heating adjusted for more complicated models. The shaded region shows the excluded area of parameter space. The plot on the left shows the effect of splitting the total dark matter density up into nf copies of the same mass field. The right plot shows the effect of relaxing the assumption of having all fields share a mass. Here we show the effect of varying the fraction of the mass in a single field that escapes the existing constraints on the dark matter mass.

The institution I visited provided me with a number of resources to better understand galactic halo structure in this model. Specifically, an adaptive resolution solver which produced simulation data I was then able to analyze. I was also responsible for writing up the results of this analysis in a paper which will hopefully be ready for publication in the coming month. My specific responsibilities involving writing code to analyze the output of simulations as well as provide an estimate of the new bounds on dark matter mass for the model we were investigating. I also had the responsibility of taking a lead in writing up the report on this work.

Beyond the technical work that we carried out this exchange was also a good opportunity to network at various German institutions in Heidelberg, Mainz, Munich, G ̈ottingen, and Vienna. This involved multiple conferences and visits arranged. These were great opportunities to speak about my research and to present my research to the broader scientific community. In total I attended three conference and a workshop, giving a presentation or poster at each. This was particularly important to do at this time because this summer immediately preceded my job application period. Since I will be applying to several positions in German institutions which I had the opportunity to actually visit during my three month stay this program offered me the chance to see what working at these institutions would be like first hand.

Learning about what it would be like to live and work in Germany involves more than just visiting potential host institutions. The opportunity also allowed me to experience things like food, cultural festivals, public transit and weekend trips to cultural sites or hiking destinations. This gives a good feel for what life outside of the working environment would be like. I was able to visit a number of major German cities, see museum and meet people living there. I was also able to go take a weekend hiking in the alps, see figure 2. This all required using the German train system and learning how to navigate the country in general.

Figure 2: Beer at one of the alpine huts in the alps. My research advisor at University of G ̈ottingen reccomended this trail in Tyrol. I have the oktoberfest hat on because I stopped in Munich to see oktoberfest beforehand.

Overall all this opportunity provided me a chance to work on an interesting project at my host institution University of G ̈ottingen, present my work at several conferences and institution visits, and experience what it would be like to live in Germany. This all came at a vital career transition point, the end of my phd, allowing me to go forward with a much stronger application and understanding of potential career options in Germany.