Sommerfeld Theory Colloquium (ASC)

Strongly correlated electron systems, i.e. systems where the interaction between electrons cannot be treated as an effective potential, are an extremely fascinating, but also very challenging topic in modern solid state physics. The challenge arises in parts due to the simultaneous importance of non-local kinetic and local correlation effects, which make it important to treat both at equal footing. For this reason Dynamical Mean Field Theory (DMFT) has in the last decades become the state of the art method for electronic structure caluclations of strongly correlated electrons as it includes local correlation effects exactly, but also respects kinetic effects in terms of an embedding approach. In this talk, we will first motivate our interest in strongly correlated materials by giving an example regarding the fascinating properties that these materials can exhibit. This will be followed by an intuitive introduction to DMFT. Finally we present results from our DMFT studies of two strongly correlated systems: BaOsO3 [1] and tetragonal CuO (t-CuO) [2]. [1] MB, Jernej Mravlje, Martin Grundner, Ulrich Schollwoeck, and Manuel Zingl, Phys. Rev. B. 103, 165133 (2021) [2] MB, B. Bacq-Labreuil, M. Grundner, S. Biermann, U. Schollwoeck, S. Paeckel, and B. Lenz, SciPost Phys., 14, 010 (2023)

In collisions of ultra-intense laser-pulse with relativistic electrons as well as in ultra relativistic heavy ion collisions at RHIC and at LHC it is possible to probe critical acceleration a=mc^3/hbar. The behavior of a particle undergoing critical acceleration challenges the limits of the current understanding of basic interactions: little is known about this physics frontier; both classical and quantum physics will need further development in order to be able to address this newly accessible area of physics. The problem of critical acceleration is closely connected to strong field particle production, Mach's Principle, Unruh and Hawking radiation.

The role of Type Ia supernovae in observational cosmology has evolved

from being ”avant-garde” in the early 1990’s until today’s mature status of precision cosmology. Several large transient surveys have been detecting supernovae routinely, near and far, with the aim of probing what is causing the accelerated expansion of the Universe.

With time, the focus has changed towards addressing the intricacies of astrophysical effects that could bias the fits of cosmological parameters,

most notably the nature of dark energy. In this talk, aimed at high-energy physics theorists(!), I will try to convey the status of

the field, high-lighting some progress and set-backs, based on studies

of the closest Type Ia SN in modern time that exploded in the

beginning of 2014 in the near-by galaxy M82.

At a singularity the continuum description of spacetime breaks down and one can hope that the microscopic constituents will be revealed. Over 50 years ago, Belinski-Khalatnikov-Lifshitz (BKL) argued that the dynamics of spacetime close to the Big Bang singularity (or inside black holes) is chaotic and inhomogeneous. I will revisit the BKL scenario within a modern understanding of quantum chaos and holographic duality. I will argue that the remarkable modular symmetries that arise in the near-singularity dynamics suggests a dual description of the start of time as a so-called "primon gas", a description that is at once both simple and also connects with deep results from number theory.

In the development of animals, tissues self-organise starting from a single cell into lay- ers, shapes and patterns. This active mechanical process operates beyond the theoretical framework of reaction-diffusion equations such as Turing patterns. At the same time, combining active driving with careful mechanical design of a system is distinct route to pattern formation and artificial functionality. Here, I will begin by introducing vertex models, a tissue model where the two dimensional cell layer is approximated by a polygonal tilings. I will then how two types of active driving can generate function: First, for polar active materials, a coupling of activity to force, a.k.a. self-alignment, is generic. Governed by the activity-elasticity interactions, it generates either flocking or oscillatory dynamics depending on the boundary conditions of the tissue. Second, mechanochemical stress feedback in cell-cell junctions arises from the catch bond dynamics of the actomyosin cortex. It allows a junction to generate a contractile force that can overcome external pulling and thus allow for an active rear- rangement or T1. In vertex and continuum models, for strong enough feedback this gives rise to convergence-extension flows where the flow is opposite the direction of mechanical polarisation, effectively generating a negative viscosity state.

A central question in fundamental physics is when an effective field theory can be consistently coupled to gravity at high energies. Over the years, various necessary conditions for this to be possible have been conjectured. String theory is a proposed framework for a quantum gravity theory and hence allows us to quantitatively test and further develop such ideas. In this colloquium I will discuss this with special emphasis on the so-called Weak Gravity Conjecture and the Swampland Distance Conjecture, or its refinement dubbed Emergent String Conjecture. Among other connections to mathematics, we will see how these proposed general principles naturally follow from the geometry of string compactifications near the boundary of moduli space and are deeply routed in string dualities. This includes situations with a minimal amount of supersymmetry in four dimensions.

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.

I will review the basic defi�nitions and ideas of the twistor program

for fundamental physics, as started by Roger Penrose around 1970. I

will give particular attention to certain conformally invariant struc-

tures involving deformed helicities, relevant to scattering amplitudes

for massless �elds. These played a role in Penrose's earliest contour

integral expressions, but have more recently been rediscovered and

greatly developed as an approach to regularization.

A unified theory for space-time and matter might be based on finite

projective geometries instead of differentiable manifolds and gauge

groups. Each point is equipped with a quadratic form over a finite Galois field which define neighbors in the finite set of points.

Due to the projective equivalence of all quadratic forms this world

is necessarily a 4-dimensional Lorentz-invariant space-time with a

gauge symmetry G(3)xG(2)xG(1) for internal points which represent elementary particle degrees of freedom. Matter appears as a

geometric distortion by an inhomogeneous field of quadrics and all

physical properties (spins, charges) of the standard model seem to

follow from its geometric structure in a continuum limit. The finiteness inevitably induces a fermionic quantization of all matter fields

and a bosonic for gauge fields. This unity of space-time and matter

was already sought 1918 by Hermann Weyl in a gauge theory as an

extension of Einstein’s general theory of relativity, but not found -

probably because of the assumption of a continuous geometry.

Protoplanetary discs are natural consequence of star formation. These discs hold the left-over material from star formation, which constitutes the reservoir from which new planetary systems may form. The fate of a new planetary is then intimately linked to the evolution and final dispersal of the disk from which is born, which determines also the striking diversity observed in extra-solar planetary systems. I will briefly review our understanding of disc dispersal via a photoevaporative wind in the context of planet formation, and show how both processes are finally dominated by the irradiation from their central star.