Sommerfeld Theory Colloquium (ASC)
130 episodes - English - Latest episode: 20 days ago - ★★★★★ - 2 ratingsThe Arnold Sommerfeld Center for Theoretical Physics organizes regular colloquia about topics of current interest in the field of theoretical physics.
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Episodes
High order correlation and what we can learn about the solution for many body problems from experiment
April 24, 2024 15:48 - 1 hour - 1.08 GB VideoThe 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 ca...
How a physical system can be turned into a self-learning machine
April 24, 2024 15:48 - 1 hour - 422 MB VideoMachine 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-processi...
How Much Structure Is Needed for Huge Quantum Speedups?
April 24, 2024 15:48 - 1 hour - 1.78 GB VideoSommerfeld Theory Colloquium
Hunting for the stochastic gravitational-wave background: Implications for astrophysics, high energy physics, and theories of gravity
April 24, 2024 15:48 - 1 hour - 1.53 GB VideoI 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 esti...
Identifying the Time Scales in Electron-Positron Production from Ultra-Strong Electric Fields
April 24, 2024 15:48 - 1 hour - 1.69 GB VideoElectron-positron pair production in ultra-strong electric fields, the Sauter-Schwinger effect, is a long-standing theoretical prediction. In this talk the Sauter-Schwinger effect will be introduced and the related field-strength and energy scales as well as the possibility to verify this effect in upcoming multi-petawatt laser facilities will be discussed. The Dirac-Heisenberg-Wigner formalism provides a fully Poincaré-covariant, non-perturbative phase space description of the Sauter-Schwing...
Influence of the fermionic exchange symmetry in the 1-particle picture
April 24, 2024 15:48 - 1 hour - 760 MB VideoIn a recent breakthrough, a complete set of constraints on fermionic occupation numbers, extending Pauli’s original exclusion principle, has been found. We provide an introduction into this new research field. In particular, we show that those generalized Pauli constraints are approximately saturated in various few-fermion systems, i.e. the vector of occupation numbers lies close to the boundary of the allowed region. Striking implications of this quasipinning phenomenon are revealed and disc...
Interplay between mechanics and chemistry in living systems
April 24, 2024 15:48 - 1 hour - 1.1 GB VideoLiving 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 no...
Is Dark Matter made of Primordial Black Holes? JWST might tell!
April 24, 2024 15:48 - 57 minutes - 352 MB VideoSommerfeld Theory Colloquium
Ising’s Challenge and the Conformal Bootstrap
April 24, 2024 15:48 - 1 hour - 1.13 GB VideoThroughout the century that has passed since Ernst Ising submitted his PhD thesis in 1924, the Ising (-Lenz) model has provided an incredibly fruitful challenge that gave rise to entirely new branches of physics and mathematics. In this colloquium I will focus on the conformal bootstrap program which was designed by Polyakov in 1974 as a mathematical method to access non-perturbative aspects of critical systems/fixed points of the renormalization groups. In the light of holography, such syst...
Lattice gauge theory insights
April 24, 2024 15:48 - 1 hour - 1.07 GB VideoVarious 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.
Lattice QCD in Regensburg
April 24, 2024 15:48 - 1 hour - 1.04 GB VideoIn Regensburg there exists a large Lattice-QCD group (SFB/TR-55) working in many fields, ranging from the development of energy efficient super-computers to specialized Lattice studies of SU(N) gauge theories with N>3 for matching to AdS/CFT predictions. The bulk of the work is focused on hadron phenomenology [generalized parton distributions (GPDs), distribution amplitudes (DAs), transverse momentum dependent parton distributions (TMDs)] and QCD thermodynamics, especially in a magnetic backg...
Limits of strong CP
April 24, 2024 15:48 - 1 hour - 1.04 GB VideoQuantum mechanical potentials with multiple classically degenerate minima lead to spectra that are determined by the pertaining tunneling amplitudes. For the strong interactions, these classical minima correspond to configurations of a given Chern-Simons number. The tunneling amplitudes are then given by instanton transitions, and the associated gauge invariant eigenstates are the theta-vacua. Under charge-parity (CP) reversal theta changes its sign, and so it is believed that CP-violating ob...
Lorentz Violation, Gravity, Dissipation and Holography
April 24, 2024 15:48 - 1 hour - 597 MB VideoLorentz 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 a...
Modeling microbial diversity
April 24, 2024 15:48 - 1 hour - 1010 MB VideoMetagenomics has revealed hundreds to thousands of microbial species coexisting in almost all microbiota. It is increasingly appreciated that microbial communities condition their own environments. To better understand the role of this environmental conditioning in promoting diversity, we physically model the population dynamics of microbes that compete for steadily supplied resources. In a model where cells require multiple nutrients, we find that population dynamics generally leads to the c...
Modern aspects of quantum physics and topology
April 24, 2024 15:48 - 1 hour - 735 MB VideoTopology 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 colo...
Multi-scale fluctuations in non-equilibrium systems
April 24, 2024 15:48 - 1 hour - 401 MB VideoUnderstanding 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 manipulatin...
Multispherical shapes, constant-mean-curvature surfaces, and the endoplasmic reticulum
April 24, 2024 15:48 - 1 hour - 641 MB VideoThe 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 indivi...
Near-Pristine Gas at High Redshifts: First Stars, Big-Bang Nucleosynthesis, and Limits on Dark Radiation
April 24, 2024 15:48 - 1 hour - 1.14 GB VideoIn this seminar, I shall describe recent work by our group on iden- tifying pockets of gas at high redshift that have undergone mini- mum processing through stars. The chemical composition of such gas still bears the imprints of the first few generations of stars that formed only a few hundred million years after the Big Bang, and thereby gives us clues to the physical properties of these still mys- terious objects which heralded the so-called ‘epoch of reionisation’. Near-pristine gas at hig...
Negative absolute temperatures for mobile particles
April 24, 2024 15:48 - 1 hour - 1.04 GB VideoAbsolute temperature, that is the fundamental temperature scale in thermodynamics, is usually bound to be positive. Under special con- ditions, however, negative temperatures - where high-energy states are more occupied than low-energy states - are also possible. In this talk, I will present a negative temperature state for motional degrees of freedom: By tailoring the Bose-Hubbard Hamiltonian we exper- imentally created an attractively interacting ensemble of ultracold bosons, which is stabl...
Neutrino Paradigm and Large Hadron Collider
April 24, 2024 15:48 - 1 hour - 632 MB VideoThe 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...
New developments in supermembrane theory
April 24, 2024 15:48 - 1 hour - 504 MB VideoThe (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 construct...
Non-equilibrium Relaxation and Aging Kinetics
April 24, 2024 15:48 - 1 hour - 586 MB VideoIf 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 tempor...
Novel Topologically Ordered Phases of Condensed Matter
April 24, 2024 15:48 - 1 hour - 608 MB VideoMuch of condensed matter physics is concerned with understanding how different kinds of order emerge from interactions between a large number of simple constituents. In ordered phases such as crystals, magnets, and superfluids, the order is understood through ”symme- try breaking”: in a crystal, for example, the continuous symmetries of space under rotations and translations are not reflected in the ground state. A major discovery of the 1980s was that electrons confined to two dimensions and...
Out-of-equilibrium phenomena from a new perspective: an Ab-Initio approach
April 24, 2024 15:48 - 1 hour - 983 MB VideoUltra-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 de...
Particle physics: Plan B
April 24, 2024 15:48 - 1 hour - 737 MB VideoParticle physics is at the crossroads. The last particle firmly predicted by the Standard Model (SM) has been discovered. In recent years many of its interactions with other known particles have been experimentally studied, again confirming the SM's predictions in large detail. However, despite this impressive success, we are sure that the SM is incomplete. The Standard Model can not explain dark matter, neutrino masses, and matter-antimatter asymmetry of the Universe, and we do know what par...
Particle Scattering and Number Theory
April 24, 2024 15:48 - 1 hour - 1.62 GB VideoFrom the softest of interactions of a magnetic field with an electron, to the most violent collisions at the Large Hadron Collider, precision quantum field theory produces numbers and functions with interesting number-theoretic properties. In many examples a co-action principle holds, an invariance under a ”cosmic” Galois group. I will provide several arenas in which this principle can be seen at work, including perhaps the richest set of theoretical data, scattering amplitudes in planar N = ...
Phenomenological and Cosmological Implications of String Theory Models
April 24, 2024 15:48 - 1 hour - 1.22 GB VideoSommerfeld Theory Colloquium
Planck mission: the 2013 cosmology results
April 24, 2024 15:48 - 1 hour - 1.19 GB VideoSommerfeld Theory Colloquium
Playing with the building blocks of the Universe
April 24, 2024 15:48 - 1 hour - 667 MB VideoThe conventional models of high energy physics place the elementary particles on a fixed or slowly evolving, nearly flat, spacetime geometry. The space foam predicted for quantum theory of gravity by A.Wheeler and S.Hawking gives a very different picture of the small scale structure of spacetime, with Planck size black holes popping out of vacuum here and there. Recent discoveries in astronomy and astrophysics, the detection of gravitational waves, exploration of Sgt A* , have confirmed the e...
Positivity constraints on theory space
April 24, 2024 15:48 - 1 hour - 469 MB VideoThe 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.
Precision at the LHC: why and how
April 24, 2024 15:48 - 1 hour - 1.38 GB VideoWith Run II, the LHC experiment already reached an unprecedented level of precision compared to previous hadron colliders. The amount of data collected in Run III and the High-Luminosity run will increase quickly and dramatically. I will discuss specific challenges to theorists that must be overcome to provide predictions that have the precision necessary to match the accuracy of data. A few novel ideas to exploit this precision directly or indirectly will also be discussed.
Precision Measurements of the Cosmic Microwave Background
April 24, 2024 15:48 - 1 hour - 1.1 GB VideoWe review the current status of measurements of the spectrum, an isotropy and polarization of the CMB, and their impact on cos- mology. We show that there is still a large discovery potential in these measurements, complementing and synergic to other cosmology observations. We also describe a selection of new measurement eff�orts, including high precision measurements of CMB polarization with ground-based, stratospheric balloon and satellite experiments, focusing on the astrophysical and tech...
Pulling Yourself by your Bootstraps in Quantum Field Theory
April 24, 2024 15:48 - 1 hour - 1.71 GB VideoQuantum field theory (QFT) is the universal language of theoretical physics, underlying the Standard Model of elementary particles, the physics of the early Universe and a host of condensed matter phenomena such as phase transitions and superconductivity. A great achievement of 20th-century physics was the understanding of weakly coupled quantum field theories where interactions can be treated as small perturbations of otherwise freely moving particles. Critical challenges for the 21st centur...
Quantum Critical Points in Metals: Non-Fermi Liquids and their Field Theoretical Description
April 24, 2024 15:48 - 53 minutes - 818 MB VideoMetals are found frequently in nature and their properties are usually very well described within Landaus Fermi liquid theory. Various strongly correlated materials exhibit strange metallic phases which do not fit into the Fermi-liquid framework, however. The theoretical description of such non-Fermi liquids remains one of the main unsolved problems in condensed matter physics. In this talk I will give an introduction to the problem and show how interesting strongly coupled field theories ari...
Quantum Gravity and the Swampland
April 24, 2024 15:48 - 1 hour - 1.53 GB VideoString theory seems to offer an enormous number of possibilities for low energy physics. The huge set of solutions is often known as the String Theory Landscape. In recent years, however, it has become clear that not all quantum field theories can be consistently coupled to gravity. Theories that cannot be ultraviolet completed in quantum gravity are said to be in the Swampland. In this talk, I'll discuss some conjectured properties of quantum gravity, evidences for them, and their applicatio...
Quantum Gravity with Anisotropic Scaling and the Multicritical Universe
April 24, 2024 15:48 - 1 hour - 1.24 GB VideoThe problem of understanding how gravity fits together with other fundamental interactions of matter has been at the forefront of the- oretical research for many decades, leading to the rich framework of string theory and M-theory. In this framework, many fundamen- tal questions are being resolved, but many remain quite mysterious, suggesting that search for novel concepts may be well justified. I review the recent concept of multicritical gravity with Lifshitz-type anisotropic scaling, and i...
Quantum Mechanics and Geometry of Spacetime
April 24, 2024 15:48 - 1 hour - 1.11 GB VideoQuantum mechanics is important for determining the geometry of spacetime. We will review the role of quantum fluctuations that determine the large scale structure of the universe. In some model universes we can give an alternative description of the physics in terms of a theory of particles that lives on its boundary. This implies that the geometry is an emergent property. Furthermore, entanglement plays a crucial role in the emergence of geometry. Large amounts of entanglement are conjecture...
Quantum simulators for fundamental physics
April 24, 2024 15:48 - 1 hour - 1.08 GB VideoThe dynamics of the early universe and black holes are fundamental reflections of the interplay between general relativity and quantum fields. The essential physical processes occur in situations that are difficult to observe and impossible to experiment with: when gravitational interactions are strong, quantum effects are important, and theoretical predictions for these regimes are based on major extrapolations of laboratory-tested physics. We will discuss the possibility to study these pr...
Quantum Theory and Realism - 'Esquisse d'un Programme'
April 24, 2024 15:48 - 1 hour - 794 MB VideoIn this lecture I propose to discuss some issues concerning the founda- tions of quantum mechanics and its interplay with space-time physics. I start by clarifying the distinction between ’realistic theories’ and ’probabilistic theories’ of Nature and sketch how the latter can often be viewed as ’deformations’ of the former. I then briefly recall some of the intriguing features of atomistic Quantum Mechanics, which belongs to the second class of theories. I attempt to describe, in con- ceptua...
Real Time Imaging of Thermal and Quantum Fluctuations
April 24, 2024 15:48 - 1 hour - 1.01 GB VideoTremendous progresses have been achieved in the last decade in real- ising and manipulating stable and controllable quantum systems, and these made possible to experimentally study fundamental questions posed in the early days of quantum mechanics. We shall theoretical discuss recent cavity QED experiments on non-demolition quantum measurements. While they nicely illustrate postulates of quantum mechanics and the possibility to implement efficient quantum state manipulations, these experiment...
Re-examining Cosmic Acceleration
April 24, 2024 15:48 - 2 hours - 1.23 GB VideoType Ia supernovae are standard (isable) candles so observing them out to cosmological distances reveals the change of the Hubble parameter with redshift. Such observations have been interpreted to mean that the expansion rate of the universe is accelerating, as if driven by a Cosmological Constant. However reanalysis of the data shows that the inferred cosmic acceleration is anisotropic and aligned with the CMB dipole - so is likely an artefact due to our being untypical observers embedded i...
Resurgence and non-perturbative physics
April 24, 2024 15:48 - 1 hour - 940 MB VideoPerturbation theory remains one of the main tools in physics, in particular in quantum theories. However, most perturbative series diverge factorially, and it is not obvious how to extract information from them. Their divergence also suggests that, in order to obtain accurate results, one might need additional non-perturbative information. The theory of resurgence has been proposed as a general framework to address these issues. In this talk I will give an introduction to this theory and will...
Revisiting the S-matrix bootstrap
April 24, 2024 15:48 - 1 hour - 1.09 GB VideoSommerfeld Theory Colloquium
R-matrix Quantization of the Ruijsenaars-Schneider Models
April 24, 2024 15:48 - 1 hour - 1.62 GB VideoI describe an algebraic scheme for quantizing the Ruijsenaars-Schneider models in the R-matrix formalism. It is based on a special parametrization of the cotangent bundle over GL(n,C). In new variables the standard symplectic structure is described by a classical (Frobenius) r-matrix and by a new dynamical r¯-matrix. Quantizing these r-matrices, I will exhibit the quantum L-operator algebra and construct its particular representation corresponding to the RuijsenaarsSchneider system. I will al...
Scattering Amplitudes from Geometry
April 24, 2024 15:48 - 1 hour - 1020 MB VideoI will review for a general audience some recent developments in our understanding of the mathematical structure of scattering amplitudes in quantum field theory. Many of these developments involve properties that have been discovered ”experimentally”: not in actual experiments, but by carrying out a tedious calculation and then observing that the result has some remarkable hidden simplicity. I will give examples of this phenomenon, and in particular I will discuss some aspects of the geometr...
Searching for Cosmic Strings in New Observational Windows
April 24, 2024 15:48 - 1 hour - 498 MB VideoMany particle physics theories beyond the Standard Model (BSM) admit topologically stable cosmic string solutions. If Nature is described by such a theory, a network of strings will form in the early universe and persist to the present time. The strings carry energy and hence lead to characteristic signatures in many observational windows. Searching for signals of strings in the sky can lead to new constraints on BSM models. Conversely, cosmic strings may also help solve some current mysterie...
Searching for New Forces Using Torsion Pendula
April 24, 2024 15:48 - 56 minutes - 860 MB VideoEquivalence principle violation, deviations from the inverse-square law of gravity, and long-range interactions between particle spins o�er powerful tests of beyond-the-standard-model physics. Using a torsion pendulum, a technique that dates to the 18th century, is still the most sensitive way to search for these signatures of new physics. I will talk about how the experiments are done and give an update on the current and future status of such torsion balance experiments in the Eot-Wash group.
Self-organization and self-assembly in biologically inspired non-equilibrium systems
April 24, 2024 15:48 - 58 minutes - 440 MB VideoSommerfeld Theory Colloquium
Sommerfeld Lecture Series
April 24, 2024 15:48 - 1 hour - 682 MB VideoIn connection with the existing and forthcoming missions dedicated to search for cosmic antimatter, the models of baryogenesis leading to an efficient creation of astronomically large antimatter objects are reviewed. It is argued that such objects may be abundant in the universe and even in the Galaxy. Their observational signatures and the prospects for discovery are discussed.
Sommerfeld Theory Colloquium
April 24, 2024 15:48 - 1 hour - 742 MB VideoA theory with such a mathematical beauty cannot be wrong: this was one of the main arguments in favor of string theory, which unifies all known physical theories of fundamental interactions in a single coherent description of the universe. But no one has ever observed strings, not even indirectly, neither the space of extra dimensions where they live. However, there are good reasons to believe that the ``hidden" dimensions of string theory may be much larger than what we thought in the past a...