**4 May 2022**

**RTG Colloquium** - Online (orig. University Oldenburg)

**14:30- 17:00 CET**

Schedule:

**14:30 - 15:30 ****Daniela Pugliese (University of Rome “La Sapienza”):** Lense-Thirring effect on accretion flow from counter-rotating tori

*Abstract*: We study the accretion flow from a counter-rotating torus orbiting a central Kerr black hole (BH). We characterize the flow properties at the turning point of the accreting matter flow from the orbiting torus, defined by the condition uφ=0 on the flow toroidal velocity. The counter-rotating accretion flow and jet-like flow turning point location along BH rotational axis is given. Some properties of the counter-rotating flow thickness and counter-rotating tori energetics are studied. The maximum amount of matter swallowed by the BH from the counter-rotating tori is determined by the background properties. The fast spinning BH energetics depends mostly on BH spin rather than on the properties of the counter-rotating fluids or the tori masses. The turning point is located in a narrow orbital corona (spherical shell), for photons and matter flow constituents, surrounding the BH stationary limit (outer ergosurface), depending on the BH spin-mass ratio and the fluid initial momentum only. The turning corona for jet-like-flow has larger thickness, it is separated from the torus flow turning corona and it is closer to the BH stationary limit. Turning points of matter accreting from torus and from jets are independent explicitly of the details of the accretion and tori model. The turning corona could be observable due to an increase of flow luminosity and temperature. The corona is larger on the BH equatorial plane, where it is the farthest from the central attractor, and narrower on the BH poles.

15:30 - 16:00 Coffee break

**16:00 - 17:00 ****Claus Kiefer (University of Cologne):** Decoherence in quantum mechanics and quantum cosmology

*Abstract*: How does the classical behaviour emerge in a world that is fundamentally described by quantum theory? The key to the answer is given by a process that was described for the first time in 1970 – decoherence. Decoherence is the irreversible emergence of classical properties of a quantum system through the unavoidable interaction with its environment.

In my talk, I give a general introduction into decoherence and present its most important theoretical and experimental applications. I discuss the situation in quantum mechanics including the relevance of decoherence for the interpretation of quantum theory. I then turn to quantum cosmology and explain how the classical appearance of the metric and matter fields can be understood in a theory of quantum gravity where arbitrary metric superpositions can occur. I also address the quantum-to-classical transition for primordial fluctuations in cosmology and point out the relevance of decoherence for the origin of the arrow of time.

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