Sommerfeld Theory Colloquium (ASC)

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High order correlation and what we can learn about the solution for many body problems from experiment Jun 10, 2026

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The knowledge of all correlation functions of a system is equivalent to solving the corresponding quantum many-body problem. If one can identify the relevant degrees of freedom, the knowledge of a finite set of correlation functions is in many cases sufficient to determine a sufficiently accurate solution of the corresponding field theory. Complete factorization is equivalent to identifying the relevant degrees of freedom where the Hamiltonian becomes diagonal. I will give examples how one can apply this powerful theoretical concept in experiment. A detailed study of non-translation invariant correlation functions reveals that the pre-thermalized state a system of two 1-dimensional quantum gas relaxes to after a splitting quench [1], is described by a generalized Gibbs ensemble [2]. This is verified through phase correlations up to 10th order. Interference in a pair of tunnel-coupled one-dimensional atomic super-fluids, which realize the quantum Sine-Gordon / massive Thirring models, allows us to study if, and under which conditions the higher correlation functions factorize [3]. This allowed us to characterize the essential features of the model solely from our experimental measurements: detecting the relevant quasi-particles, their interactions and the different topologically distinct vacuum-states the quasi-particles live in. The experiment thus provides a comprehensive insight into the components needed to solve a non-trivial quantum field theory. Our examples establish a general method to analyse quantum systems through experiments. It thus represents a crucial ingredient towards the implementation and verification of quantum simulators. Work performed in collaboration with E.Demler (Harvard), Th. Gasenzer und J. Berges (Heidelberg). Supported by the Wittgenstein Prize, the Austrian Science Foundation (FWF): SFB FoQuS: F40-P10 and the EU: ERC-AdG QuantumRelax [1] M. Gring et al., Science, 337, 1318 (2012); [2] T. Langen et al., Science 348 207-211 (2015). [3] T. Schweigler et al., Nature 545, 323 (2017), arXiv:1505.03126

Arnold Sommerfeld Theory Colloquium Jun 10, 2026

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A network of ground-based interferometric gravitational wave detectors (LIGO/VIRGO/GEO/...) is currently taking data near its planned sensitivity. Coalescing black hole binaries are among the most promising, and most exciting, gravitational wave sources for these detectors. The talk will review the theoretical and experimental challenges that must be met in order to successfully detect gravitational waves from coalescing black hole binaries, and to be able to reliably measure the physical parameters of the source (masses, spins, ...).

The Many Faces of Conformal Interfaces Jun 10, 2026

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Conformal interfaces are the long-distance limits of domain walls. They play a role in condensed-matter physics, and could be also rel- evant for theories of gravity. I will review some recently-developed techniques for analyzing their properties, and will discuss their pos- sible applications.

Out-of-equilibrium phenomena from a new perspective: an Ab-Initio approach Jun 10, 2026

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Ultra-fast optical spectroscopy is a powerful tool for the observation of dynamical processes in several kind of materials. The basic time- resolved optical experiment is the so-called “pump-probe”: a first light pulse, the “pump”, resonantly triggers a photo-induced process. The subsequent system evolution can be monitored, for example, by the time–dependent transmission changes of a delayed “probe” pulse. The pump pulse photon energy, spectral width and peak intensity cre- ates a certain density of electron-hole pairs in a more or less localized region of space. After the creation of the initial carrier density the time evolution of the single-particle and many-particle excitations is now governed by a non-trivial interplay between electron-electron and electron-phonon scatterings. In this talk I will present a novel approach based on the merging of Non-Equilibrium Green’s func- tion theory and Density Functional Theory to investigate the carrier dynamics following a pump excitation. The case of bulk Silicon, a paradigmatic indirect gap semiconductor, is studied by using the Baym-Kadanoff equations. Both the electron-electron (e-e) and elec- tronphonon (e-p) self-energies are calculated fully Ab-Initio by using a semi-static GW approximation in the e-e case and a Fan self-energy in the e-p case. By using the generalized Baym-Kadanoff ansatz the two-time evolution is replaced by the only dynamics on the macro- scopic time axis. The enormous numerical difficulties connected with a real-time simulation of realistic systems is overcomed by using a completed collision approximation that further simplifies the mem- ory effects connected to the time evolution. The carrier dynamics is shown to reduce in such a way to have stringent connections to the well-known equilibrium electron-electron and electron-phonon self- energies. This link allows to use general arguments to motivate the relative balance between the e-e and e-p scattering channels on the basis of the carrier energies.

Non-equilibrium Relaxation and Aging Kinetics Jun 10, 2026

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If systems characterized by slow (algebraic) relaxation are prepared in an out-of-equilibrium initial state, one can observe a "physical aging regime" in the ensuing approach to equilibrium that is governed by broken time translation invariance and non-trivial, often universal scaling laws. Dynamical systems near a critical point constitute prototypical and now well-understood examples. Indeed, measuring critical exponents in the intermediate aging rather than the asymptotic stationary temporal regime is now a standard numerical tool. In this talk, I will first apply these concepts to simple driven lattice gases that relax towards non-equilibrium stationary systems displaying generic scale invariance. The expected simple aging behavior in the two-time density auto-correlation function is verified through Monte Carlo simulations in one, two, and three dimensions. Next I shall address the continuous non-equilibrium phase transition in driven Ising lattice gases in two dimensions. Whereas the temporal scaling of the density auto-correlation function in the non-equilibrium steady state does not allow a precise measurement of the associated critical exponents, these can be accurately determined from the aging scaling of the two-time auto-correlations and the order parameter evolution following a quench to the critical point. In the second part of the talk, I will present numerical results for the non-equilibrium relaxation kinetics of interacting magnetic flux lines in disordered type-II superconductors at low temperatures and low magnetic fields, represented by means of a three-dimensional elastic line model. Investigating the vortex density and height auto-correlations as well as the flux line mean-square displacement allows us to carefully disentangle different relaxation mechanisms (e.g., vortex line fluctuations and positional relaxation), and to assess their relative impact on the kinetics of dilute vortex matter at low temperatures. We observe the emergence of genuine glassy dynamics, caused by the competing effects of vortex pinning and long-range repulsive interactions between the flux lines. We contrast the effects of random point-like pinning centers and correlated columnar defects. We also compare data from Monte Carlo simulations with results from Langevin molecular dynamics.

Cosmological Symmetry Breaking as Origin of the Hot Early Universe Jun 10, 2026

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The decay of a false vacuum of unbroken B-L, the difference of baryon and lepton number, is an intriguing and testable mechanism to gen- erate the initial conditions of the hot early universe. If B-L is broken at the grand unification scale, the false vacuum phase yields hybrid inflation, ending in tachyonic preheating. The dynamics of the B-L breaking Higgs field and thermal processes produce an abundance of heavy neutrinos whose decays generate entropy, baryon asymmetry and dark matter.

Turbulence: scaling and beyond Jun 10, 2026

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This lecture is aimed at a rather broad audience including under- graduates. It will discuss scaling arguments, what they can achieve (Kolmogorov’s -5/3 law, etc.) and what they miss (fractals, Etc).

Lorentz Violation, Gravity, Dissipation and Holography Jun 10, 2026

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Lorentz non-invariance in quantum field theory is reconsidered as well as its interplay with gravity, string theory, diffeomorphism invariance and changing reference frames. We clarify these issues, and argue that Lorentz violation is always an environmental effect. We provide a holographic view of the breaking, and its connection to Horava- Lifshitz type of gravitational theories. We also argue that dissipation is always a signal of Lorentz violation. We provide calculations of dissipation at strong coupling.

Neutrino Paradigm and Large Hadron Collider Jun 10, 2026

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The physics of elementary particles is governed by symmetries. A particular symmetry stands out: the one between left and right, called parity. Its breaking in beta decay created a bombshell more than fifty years ago, and ultimately led to the creation of the Standard Model of particle interactions, whose final crowning confirmation is to be provided by the Large Hadron Collider (LHC) at CERN. The Standard Model is based on the premise of parity being broken al- ways, at all energies. I argue, on the contrary, that in nature left-right symmetry is fundamental, and that at high energies of the LHC one could actually see its restoration in full glory. I show how this would probe the nature of neutrino, through the spectacular signatures of lepton number violation.

Application of Reflection Positivity: Graphene and Other Examples Jun 10, 2026

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Reflection positivity is a useful tool in statistical mechanics and con- densed matter physics. A recent application is to the determination of the possible distortions of the hexagonal graphene lattice. Other applications, such as to potential theory, the flux-phase problem, Peierls instability and stripe formation, will also be given.

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