Mathematical and Theoretical Physics Seminar (MTPS)

Jacobs University, Spring 2021

Organized by Stefan Kettemann, Sören Petrat, and Peter Schupp

Usual time: Thursdays, 13:00-14:00

Location: for most of the semester the seminar will be online (access data will be sent around to the mailing list shortly before the talks; please write an email to Sören Petrat (s.petrat AT for the access data to specific talks or to be added to the mailing list).

All times are German time zone.

Date Talk

February 18, 2021, 13:00-14:00 (online)

Eva Hackmann (Center of Applied Space Technology and Microgravity (ZARM) at Bremen University)

Title: Equilibrium Configurations of Fluids around Black Holes

Abstract: The most luminous energy sources in our universe are active galactic nuclei, which are driven by the accretion of matter onto a supermassive black hole of millions to billions of solar masses. The accreting matter is mainly orbiting the black hole in form of an accretion disk. As the gravitational field close to the black hole is very strong, accretion disks may serve as a system to test our current understanding of the theory of gravity.
We will first review some basic aspects of General Relativity, that is currently the best available theory of gravity, and then discuss the construction of fluid configurations in strong gravitational fields. In general, these configurations are described by a set of partial differential equations derived from energy conservation and Maxwell equations. The fluid configurations can serve as a simplified model to understand some of the basic processes in accretion disks, and to study the interplay of electromagnetic and gravitational forces in these processes.

March 4, 2021, 13:00-14:00 (online)

David Mitrouskas (IST Austria)

Effective Dynamics of Tracer Particles in a Dense Fermi Gas

Abstract: We discuss the dynamics of few tracer particles in a d-dimensional box coupled to N fermions via a suitable pair interaction. After taking the large volume limit at positive Fermi momentum we consider the regime of high density, that is, large Fermi momentum. Assuming that the fermions are initially in the ground state of the kinetic energy, we show that a single tracer particle effectively decouples from the fermions and evolves like a free particle. We explain that this is based on a separation of scales between the tracer particle and the fast electrons at the Fermi surface. In the rest of the talk we show how the picture changes for more than one tracer particle and/or if one starts with an excited state of the fermions.

March 11, 2021, 13:00-14:00 (online)

Jan Olaf Mirko Härter (Niels Bohr Institute, University of Copenhagen; Jacobs University; Leibniz-Zentrum für Marine Tropenforschung)

Criticality and bistability in the tropical convective cloud field

Abstract: Whereas Rayleigh-Bénard convection is a classical problem in fluid dynamics and complex systems, atmospheric moist convection harbors a number of additional phenomena, such as large-scale segregation into cloudy and cloud-free subregions (known as convective self-aggregation) or the emergence of mesoscale convective systems - self-organized clusters of convective cells. Treating the population of convective cells as a form of interacting particle system, we discuss several simple toy models, which highlight some mechanisms involved in tropical cloud organization. We make contact to results obtained from idealized fluid dynamics simulations of the tropical atmosphere and highlight, where discrepancies between simulations and observations exist and could be bridged.

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