My background:

Roughly speaking, in my doctoral studies I consider models of the universe filled with Vlasov matter - a matter model to describe for example galaxy clusters. I had observed that a group of Japanese researchers around Tomohiro Harada had published work in which they studied the system by numerical means. I also heard a member of the group, Chulmoon Yoo, talking at a conference in Vienna, in February 2017. This made me very curious to learn about their insights into the nature of the equations and their experiences with numerics, to get new inspiration for my own ongoing numerical project or possible analytical work. In Japan I could indeed solve some problems and make progress. I wrote code for a solver of the Vlasov equation based on the particle in cell method and learned strategies to solve the constraint equations.

Accomplishments and experiences I would never have gotten unless I joined the Summer Program:

At several universities I gave talks and always find a very interested audience. The researchers in Japan were often used to different approaches of General Relativity from my research environment in Europe. This led to a fruitful exchange and some concrete project ideas that were not expected or planned. Most of all, I want to mention a project that I started towards the end of my stay together with my host professor, Tomohiro Harada. We had discussed several times some unique results for matter solutions of the Einstein equations. A physical interpretation of these results can be that if a star is not rotating, it has to be spherically symmetric. We want to apply a mathematical theorem proved by R. Beig and W. Simon to establish the same for globular clusters. This means if a globular cluster does not change its overall shape and is not rotating, it must be spherically symmetric.

Message for future participants:

For me the JSPS summer program was a very enriching and nice experience. It was very well organized and I felt well taken care of. I know that the atmosphere at the department can be very different at different institutions but I perceived it as open, friendly, social and with normal working hours. Of course there are many small cultural pitfalls but that is part of the experience and in the frame of the summer program I never felt awkward or alone.

Name: Maximilian Thaller

Title: Ph.D. Student

Institution: Chalmers University of Technology

Host University in Japan: Rikkyo University