Sommerfeld Theory Colloquium (ASC)

After a short introduction to the swampland program and the challenges one faces in explicit tests of some conjectures, this talk will focus on the computation of periods and their application to the swampland program. A detailed understanding of periods allows to answer questions about the existence of solutions or the finiteness of the string landscape, as well as explicit constructions of models. Moreover, applications of periods outside of string compactifications are discussed, such as the computation of Feynman integrals, the tameness of QFTs and the appearance of periods in many other physical systems.

Feynman integrals are indispensable for precision calculations, not only for high-energy particle physics experiments, but also for example for QED precision experiments at lower energies or precision studies in gravitational wave physics. In recent years there has been a significant progress in our abilities to compute Feynman integrals, revealing a rich and fascinating mathematical structure, relating Feynman integrals to (algebraic) geometry. In this talk I will review these recent developments.

Wetting of liquid phases, such as water drops condensing at the surface of plant leaves, is ubiquitous in our daily life. Interestingly, the physics of wetting also plays a crucial role in our cells. Droplets composed of proteins can wet specific target sites in living cells and locally enrich biomolecules for specific chemical processes. Many droplet-forming proteins can also bind to membrane surfaces. Binding in cells is often chemically active since it is maintained away from equilibrium by supplying energy and matter. This non-equilibrium setting suggests a plethora of physical phenomena of soft condensed phases at biological interfaces.

To investigate such phenomena, we derive the non-equilibrium thermodynamic theory of active wetting. By means of this theory, we show that active binding significantly alters the wetting behavior leading to non-equilibrium steady states with condensate shapes reminiscent of a fried egg or a mushroom. We further show that condensate shapes can switch upon changing the strength of active binding. The origin of such anomalous condensate shapes can be explained by an electrostatic analogy, where binding sinks and sources correspond to electrostatic dipoles along the triple line. This analogy suggests a general analogy between chemically active systems and electrodynamics.

The asymptotic structure of gravity in the asymptotically flat case will be described in four and higher spacetime dimensions by making central use of the Hamiltonian formalism. Special emphasis will be paid to the case D=5. How the relevant infinite-dimensional asymptotic symmetry group (BMS group) emerges at spatial infinity will be explained. Non-linear structures which appear in five (and higher) spacetime dimensions will be discussed.

Machine learning using artificial neural networks is revolutionizing many areas of science and technology. This increases the urgency for exploring alternatives to artificial neural networks running on digital hardware. These alternatives might eventually be faster and/or more power-efficient. With this in mind, we ask the question whether one can identify a general principle that would enable a nonlinear physical system to become a self-learning machine - i.e. a physical information-processing device where internal degrees of freedom self-adjust by physical interactions to learn a desired input-output relation. In this talk, I will present our recent idea on how this might be achieved for arbitrary time-reversal-invariant Hamiltonian systems. I will introduce the principle of 'Hamiltonian Echo Backpropagation', and demonstrate how efficient learning could be possible in a wide class of physical systems.

See: Self-learning Machines based on Hamiltonian Echo Backpropagation,

Victor Lopez-Pastor, Florian Marquardt, arXiv 2103.04992 (2021)

It has long been expected that the symmetry structure of quantum gravity is highly constrained. In particular it has been conjectured that global symmetries do not exist, and also that there must exist objects carrying all possible gauge charges. Until recently however there has been no systematic way of deriving such statements. In this talk I'll explain how these two conjectures can be derived in the special case of quantum gravity with negative cosmological constant, and also argue they are true more generally in any theory of quantum gravity where the evaporation of black holes is a unitary process. Along the way I'll clarify what is really meant by ``global'' and ``gauge'' symmetries, consider possible implications of these conjectures for particle physics, and present a new formula counting how many microstates of a black hole transform in each representation of a finite gauge group.