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Calendar of Physics Talks Vienna
| Directly computing reduced density matrices with influence functionals |
| Speaker: | Christian Käding (Atominstitut, TU Wien) |
| Abstract: | The field theory of open quantum systems has ample applications in areas like particle or nuclear physics, cosmology and quantum gravity. Open quantum systems are commonly described by reduced density matrices, which are obtained by tracing out the environmental degrees of freedom, and whose evolution is given by quantum master equations. Solving such equations often poses an intricate or even analytically impossible task. As a way to circumvent such problems, we will present a first principle-based and practicable formalism which allows for the direct computation of reduced density matrix elements without having to consider a master equation. It is based on techniques from non-equilibrium quantum field theory like thermo field dynamics, the Schwinger-Keldysh formalism and the Feynman-Vernon influence functional. As a simple example, we will focus on a scalar field system interacting wit |
| Date: | Wed, 01.03.2023 |
| Time: | 16:15 |
| Duration: | 60 min |
| Location: | Atominstitut, Stadionallee 2, 1020 Wien |
| Contact: | Christian Käding |
| Structure formation in slowly expanding cosmological fluids |
| Speaker: | Maximilian Ofner (Univ. Wien) |
| Abstract: | Matter structures are among the key observations on large scales. Hence their formation, or lack thereof, in certain mathematical models provides insight into whether these models are physically valid. In this talk we explore structure formation utilizing the tools of modern PDE analysis. Due to work by D. Christodoulou, it is known that the relativistic Euler equations are unstable for a rather comprehensive class of equations of state on Minkowski space. However, solutions exist globally for exponentially expanding FLRW-type models or even power law expansion, as was explored in the previous decade by J. Speck among many others. In our paper on dust as well as our followup on massive fluids, we prove that the homogeneous fluid solutions coupled to the Milne-universe are fully nonlineary stable solutions to the coupled Euler-Einstein-system with a linear equation of state. |
| Date: | Thu, 02.03.2023 |
| Time: | 15:30 |
| Duration: | 60 min |
| Location: | Seminarraum A, Waehringer Strasse 17, 2. Stock |
| Contact: | P. Chrusciel, D. Fajman |
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