Sommerfeld Theory Colloquium (ASC)

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The Nobel Prizes in Physics in 1932/33: Heisenberg, Schrödinger and Dirac Jun 22, 2023

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The Nobel Prize in Physics in 1930 was awarded to Raman for the discovery of the effect named after him. The next time physics prizes were announced was in November 1933, which makes this the longest peace-time gap in the history of the Nobel Prize in Physics. Considering that the 1932 year’s prize was awarded in 1933 to Heisenberg and the 1933 year’s prize to Schrödinger and Dirac for their contributions to the new quantum mechanics, this gap is the more puzzling. I will describe, based on archive material, the struggle facing the Nobel Committee during those years, and how it eventually arrived at a name combination comprising three of the greatest physicists of the twentieth century. I will also describe briefly the three Nobel Prizes concerning quantum mechanics that followed later, in 1945, 1954 and 2022.

Modern aspects of quantum physics and topology Jun 15, 2023

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Topology is one of the most recent branches of mathematics and has entered fully into the most modern aspects of theoretical physics: quantum computation. In this colloquium an elementary approach to the role of topology in quantum physics and its implications for exotic states of quantum matter is provided. Topology helps to solve the essential problem of quantum computation: to battle its fragility in order to benefit from its enormous potential possibilities. After showing topological color codes and their experimental realization, future challenges are addressed by fracton models involving the discovery of new quantum phases of matter beyond the well-known topological phases that were recognized with the Nobel Prize in Physics in 2016.

Positivity constraints on theory space May 25, 2023

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The bootstrap program leverages symmetry and positivity to carve out the space of consistent quantum theories. In this talk I will highlight some of its recent successes, ranging from the numerical solution of statistical models at criticality to universal constraints on quantum gravity.

Anomalous metals Feb 08, 2023

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The observation of metallic ground states in a variety of two-dimensional electronic systems poses a fundamental challenge for the theory of electron fluids. I will analyze evidence for the existence of a regime, which we call the “anomalous metal regime," in diverse 2D superconducting systems driven through a quantum superconductor to metal transition by tuning physical parameters such as the magnetic field, the gate voltage in the case of systems with a MOSFET geometry, or the degree of disorder. The principal phenomenological observation is that in the anomalous metal, as a function of decreasing temperature, the resistivity first drops as if the system were approaching a superconducting ground state, but then saturates at low temperatures to a value that can be orders of magnitude smaller than the Drude value. The anomalous metal also shows a giant positive magneto-resistance. This behavior is observed in a broad range of parameters. I will exhibit, by theoretical solution of a model of superconducting grains embedded in a metallic matrix, that as a matter of principle such anomalous metallic behavior can occur in the neighborhood of a quantum superconductor-metal transition. However, I will also argue that the robustness and ubiquitous nature of the observed phenomena are difficult to reconcile with any existing theoretical treatment and speculate about the character of a more fundamental theoretical framework.

Multispherical shapes, constant-mean-curvature surfaces, and the endoplasmic reticulum Jan 18, 2023

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The cells of our body are divided up into separate subcompartments by fluid membranes with a thickness of only a few nanometers. Even though these membranes provide robust barriers for the exchange of molecules between different compartments, they can easily remodel their shape and topology. [1] A particularly interesting example of shape remodeling is the formation of multispherical shapes which represent constant- mean-curvature surfaceswith two values of the mean curvature. [2] The individual spheres are connected by membrane necks which are crucial for topology remodeling by membrane fission and fusion. Multispherical shapes can attain many distinct patterns with multispherical junctions. The latter geometry is reminiscent of the endoplasmic reticulum, a fascinating organelle that forms a large network of membrane nanotubes connected by three-way junctions. [1] R. Lipowsky. Remodeling of Membrane Shape and Topology by Curvature Elasticity and Membrane Tension. Adv. Biology 6, 2101020 (2022) [2] R. Lipowsky. Multispherical shapes of vesicles highlight the curvature elasticityof biomembranes. Adv. Colloid Interface Sci. 301, 102613 (2022)

New developments in supermembrane theory Jan 16, 2023

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The (unique) maximally extended D=11 supermembrane theory stands out as a candidate for the non-perturbative unification of superstring theory. In this talk I will review some basic features, in particular the light-cone gauge reformulation of the theory as the N-->\infty limit of the maximally supersymmetric SU(N) matrix model, and present new evidence for the existence of the N-->\infty limit, using a path integral formulation. I will also touch on several open issues, such as the construction of supermembrane vertex operators.

Multi-scale fluctuations in non-equilibrium systems Dec 15, 2022

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Understanding how fluctuations propagate across spatial scales is central to our understanding of inanimate matter from turbulence to critical phenomena. In contrast to these systems, many non-equilibrium systems are organised into a spatial hierarchy of nested processes on different spatial scales, including biological and robotic systems. In this talk, I will discuss physical principles underlying the propagation of fluctuations in these multi-scale systems. I will also show how manipulating probability fluxes across spatial scales is used to perform biological signal processing.

Interplay between mechanics and chemistry in living systems Dec 08, 2022

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Living systems interact with their environment by exerting mechanical forces and exchanging chemical substances. By fueling nonequilibrium reactions and driven molecular transport, cells dynamically create internal protein patterns (symmetry breaking) which, in turn, control cell mechanics and force generation. Here, we discuss some examples and consequences of such a mechanochemical coupling, ranging from proteins that cooperatively bind and bend membranes, to protein patterns that elicit nonspecific cargo transport via driven diffusive fluxes on planar membranes. Finally, on much larger scales, we discuss how active cells can control tissue shape via their broken symmetry and, specifically, through their orientation.

Deciphering the Beginning Dec 01, 2022

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The cosmic microwave background contains a wealth of information about cosmology as well as high energy physics. It tells us about the composition and geometry of the universe, the properties of neutrinos, dark matter, and even the conditions in our universe long before the cosmic microwave background was emitted. After a general introduction, I will turn to the search for primordial gravitational waves with CMB observations and gravitational wave observatories.

Emergence of geometry and meaning, through gauge and strings dynamics Nov 16, 2022

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I will discuss the statistical physics of random growth processes which, on the one hand, model the non-perturbative gauge dynamics, emergence of space geometry in string theory on the other, yet could also model the evolution of language(s).

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