Effective equations for large systems of particles or waves

Job Candidate Talk
Monday, January 23, 2023 - 11:00am for 1 hour (actually 50 minutes)
Skiles Room 006
Ioakeim Ampatzoglou – NYU Courant Institute – ioakampa@nyu.eduhttps://cims.nyu.edu/~ia847/
Michael Loss

Understanding the behavior of large physical systems is a problem of fundamental importance in mathematical physics. Analysis of systems of many interacting particles is key for understanding various phenomena from physical sciences (e.g. gases in non-equilibrium, galactic dynamics) to social sciences (e.g. modeling social networks). Similarly, the description of systems of weakly nonlinear interacting waves, referred to as wave turbulence theory, finds a wide range of applications from solid state physics and water waves to plasma theory and oceanography. However, with the size of the system of interest being extremely large, deterministic prediction of its behavior is practically impossible, and one resorts to an averaging description. In this talk, we will discuss about kinetic theory, which is a mesoscopic framework to study the qualitative properties of large systems. As we will see, the main idea behind kinetic theory is that, in order to identify averaging quantities of large systems, one studies their asymptotic behavior as the size of the system tends to infinity, with the hope that the limiting effective equation will reveal properties observed in a system of large, but finite size. We will focus on the Boltzmann equation, which is the effective equation for systems of interacting particles, and its higher order extensions, as well as the kinetic wave equation which describes systems of many nonlinearly interacting waves.