Sommerfeld Theory Colloquium (ASC)

Various aspects of lattice gauge theory will be briefly discussed including, general principles, sources of systematic errors, dynamical fermions, QCD phenomenology, the FLAG project and, if time allows, some applications of lattice theory to other non-perturbative BSM phenomena.

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.

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.

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.

I will first define the stochastic gravitational-wave background (SGWB) and highlight the method we are using to detect it in the presence of correlated magnetic noise. I will then discuss astrophysical (compact binary coalescences) and cosmological (cosmic strings, first-order phase transitions) sources and report on the current constraints imposed from a non-detection during the last observing run of the LIGO/Virgo/KAGRA collaboration. I will also address the question of a simultaneous estimation of astrophysical and cosmological SGWB. Then I will present a search for circularly polarised SGWB and its relation to early universe cosmology. Finally, I will discuss how the SGWB can provide tests for gravity theories, including quantum gravity proposals.

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.

Condensed matter provides us deep insights into quantum physics.

Giving just two examples, wave-corpuscle duality manifests itself in

spectroscopy of strongly correlated systems as coexistence of itinerant

and atomic-like features, and graphene and other Dirac materials

provide a natural playground to study vacuum reconstruction, Klein

tunneling and other fundamental quantum relativistic phenomena.

Electron-photon interaction is the key tool to understand this rich

and nontrivial physics.

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.

Majorana fermions are spatially localized superpositions of electron and hole excitations in the middle of a superconducting energy gap. These unusual particles have been predicted to occur at the interface between a magnetic and superconducting electrode, in contact with a topological insulator (such as a Bi crystal or a HgTe quantum well). A single qubit can be encoded nonlocally in a pair of spatially separated Majorana fermions. Such Majorana qubits are in demand as building blocks of a topological quantum computer, but direct experimental tests of the nonlocality remain elusive.

We propose a method to probe the nonlocality by means of crossed Andreev reflection, which is the injection of an electron into one bound state followed by the emission of a hole by the other bound state. The resulting splitting of a Cooper pair by the Majorana qubit produces a pair of excitations that are maximally entangled in the momentum (rather than the spin) degree of freedom, and might be used as "flying qubits" in quantum information processing.

The hard-disk model has exerted outstanding influence on computational

physics and statistical mechanics. Decades ago, hard disks

were the first system to be studied by Markov-chain Monte Carlo

methods and by molecular dynamics. It was in hard disks, through

numerical simulations, that a two-dimensional melting transition was

first seen to occur even though such systems cannot develop long-range

crystalline order. Analysis of the system was made difficult

by the absence of powerful simulation methods. In recent years, we

have developed powerful Monte Carlo algorithms for hard disks and

related systems. I will in particular show how the event-chain Monte

Carlo algorithm has allowed us to prove that hard disks melt with a

first-order transition from the liquid to the hexatic and a continuous

transition from the hexatic to the solid. I will finally describe how a

new factorized Metropolis filter transforms the event-chain algorithm

into a paradigm for general Monte Carlo calculations. First results

with the generalized algorithm have allowed us to establish the phase

diagram for two-dimensional soft disks and Yukawa particles.