Sommerfeld Theory Colloquium (ASC)
129 episodes - English - Latest episode: 3 months ago - ★★★★★ - 2 ratingsThe Arnold Sommerfeld Center for Theoretical Physics organizes regular colloquia about topics of current interest in the field of theoretical physics.
Homepage Apple Podcasts Google Podcasts Overcast Castro Pocket Casts RSS feed
Episodes
Ising’s Challenge and the Conformal Bootstrap
February 08, 2024 13:45 - 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...
Resurgence and non-perturbative physics
February 08, 2024 13:34 - 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...
Lorentz Violation, Gravity, Dissipation and Holography
February 07, 2024 16:36 - 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...
Lattice gauge theory insights
February 07, 2024 16:36 - 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.
Application of Reflection Positivity: Graphene and Other Examples
February 07, 2024 16:36 - 1 hour - 604 MB VideoReflection 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.
Limits of strong CP
February 07, 2024 16:36 - 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...
A Closer Look at Black Holes
February 07, 2024 16:36 - 1 hour - 949 MB VideoSeveral new techniques are currently being employed to probe the strong gravitational fi�eld in the vicinity of black holes. Long baselineinterferometry at sub-millimeter wavelengths sets constraints on the silhouette of the black holes in the Galactic center (SgrA*) and M87. Stars which get tidally disrupted as they orbit too close to a single black hole are being discovered at cosmological distances. Electromagnetic counterparts of black hole binaries in galaxy mergers are being identifi�ed...
Chemically Active Wetting
February 07, 2024 16:36 - 1 hour - 344 MB VideoWetting 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 b...
Anomalous metals
February 07, 2024 16:36 - 1 hour - 319 MB VideoThe observation of metallic ground states in a variety of two-dimensional electronic systems poses a fundamental challenge for the theory of electron fluids. I will analyze evidence for the existence of a regime, which we call the “anomalous metal regime," in diverse 2D superconducting systems driven through a quantum superconductor to metal transition by tuning physical parameters such as the magnetic field, the gate voltage in the case of systems with a MOSFET geometry, or the degree of dis...
Cosmology with Type Ia Supernovae: where do we stand today?
February 07, 2024 16:36 - 1 hour - 1000 MB VideoThe 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 ...
Black holes as harbingers of new gravitational physics
February 07, 2024 16:36 - 1 hour - 1.33 GB VideoThe apparent crisis of black holes inconsistency with foundational physical principles provides a sharp focus for the conflict between quantum mechanics and classical spacetime. Various resolutions have been proposed; a very plausible one is that small interactions can transfer sufficient information between the black hole and outgoing radiation, with a quantum enhancement from the enormous number of black hole states. Such interactions must however violate conventional notions of locality, p...
Black Holes, Quantum Information, and Unification
February 07, 2024 16:36 - 1 hour - 1.58 GB VideoThe study of black holes has revealed a deep connection between quantum information and spacetime geometry. Its origin must lie in the quantum theory of gravity, which offers a valuable hint in our search for a unified theory. Precise formulations of this relation recently led to new insights in Quantum Field Theory, some of which have been rigorously proven. An important example is our discovery of the first universal lower bound on the local energy density. The energy near a point can be ne...
Branes, Islands, and Massive Gravitons
February 07, 2024 16:36 - 1 hour - 1.17 GB VideoQuantum Gravity in Anti-de Sitter space coupled to a non-gravitating bath has been the setting for novel approaches to the black-hole information paradox. Works from 2 decades ago in the context of Randall-Sundrum braneworlds makes it clear that this system necessarily describes massive gravitons: as soon as one couples AdS gravity to a bath, the graviton gets a mass. These two phenomena are intrinsically linked. We'll review old work that led to this conclusion, and present novel results tha...
Can a quantum computer solve optimization problems more Efficiently than a classical computer?
February 07, 2024 16:36 - 1 hour - 958 MB VideoIn this talk I will discuss connections between the physics of complex systems such as spin glasses and attempts to solve optimization problems by ”Adiabatic Quantum Computing” (AQC), a version of ”Quantum Annealing” (QA). An optimization problem is one in which one has to minimize (or maximize) an energy function in which there is competition between different terms so no single configuration of the variables minimizes each term in the energy. In statistical physics this competition is calle...
Extreme Light and Quantum Fields
February 07, 2024 16:36 - 1 hour - 1.04 GB Video2015 is the International Year of Light, and of its purposes is “to raise awareness of optical technologies”. One such technology, high-power lasers of the petawatt class and beyond, provides the most intense light sources created by humankind so far. The intensities and field strengths in question are in excess of 1022 W/cm2 and 1014 V/m, respectively magnitudes that correspond to concentrating the total solar radiation on a pinhead. This talk will present an overview of the uses and consequ...
Exact, Broken and Approximate Symmetries
February 07, 2024 16:36 - 56 minutes - 875 MB VideoSommerfeld Theory Colloquium
Chiral symmetry breaking, emergent Higgs mechanism, and critical matter
February 07, 2024 16:36 - 1 hour - 1.03 GB VideoThe upshot of extensive studies of �uctuations in condensed matter systems is that their qualitative importance is typically con#ned to isolated critical points of continuous transitions between phases of matter. This conventional wisdom also predicts the number of low energy Goldstone modes based on the so-called “G/H” pattern of symmetry breaking. I will discuss a class of systems, some quite wellknown, that violate this standard paradigm. Namely, they exhibit a fewer than “G/H” number of l...
Conjectures on Quantum Gravity and their Realisation in String Theory
February 07, 2024 16:36 - 1 hour - 558 MB VideoA 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 C...
Contacting the moon
February 07, 2024 16:36 - 1 hour - 1.13 GB VideoThe restricted three body problem has an intriguing dynamics. Glo- bal surfaces of section are a tool to reduce the study of the dynamics on a three dimensional energy hypersurface to the study of an area preserving map of a two dimensional surface. The existence of such a global surface of section is far from obvious. So far mostly per- turbative methods have been used to prove its existence. However, recently developed global tools originating from Gromov-Witten the- ory combined with the f...
Cosmological Symmetry Breaking as Origin of the Hot Early Universe
February 07, 2024 16:36 - 1 hour - 597 MB VideoThe 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.
High order correlation and what we can learn about the solution for many body problems from experiment
February 07, 2024 16:36 - 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...
Critical Acceleration
February 07, 2024 16:36 - 1 hour - 598 MB VideoIn 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 accessib...
Deciphering the Beginning
February 07, 2024 16:36 - 1 hour - 430 MB VideoThe cosmic microwave background contains a wealth of information about cosmology as well as high energy physics. It tells us about the composition and geometry of the universe, the properties of neutrinos, dark matter, and even the conditions in our universe long before the cosmic microwave background was emitted. After a general introduction, I will turn to the search for primordial gravitational waves with CMB observations and gravitational wave observatories.
Effects of Dark Matter linear in Interaction Strength
February 07, 2024 16:36 - 46 minutes - 708 MB VideoLow-mass boson dark matter particles produced after the Big Bang form a classical field and/or topological defects. Effects produced by the interaction of ordinary matter with dark matter may be first power in the underlying interaction strength rather than the second power. This may give a big advantage, since the dark matter interaction constant is extremely small. Limits on certain types of dark matter have been improved up to 15 orders of magnitude. New experiments are proposed.
Effects of electronic correlations in BaOsO3 and tetragonal CuO
February 07, 2024 16:36 - 1 hour - 1.12 GB VideoStrongly 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 ...
Einstein and Quantum Mechanics: It's Not What You Think
February 07, 2024 16:36 - 1 hour - 1.19 GB VideoEinstein is well known for his rejection of quantum mechanics in the form it emerged from the work of Heisenberg, Born and Schrodinger in 1926. Much less appreciated are the many seminal contributions he made to quantum theory prior to his �final scientifi�c verdict, that the theory was at best incomplete. In this talk I present an overview of Einsteins many conceptual breakthroughs and place them in historical context. I argue that Einstein, much more than Planck, introduced the concept of q...
Emergence of geometry and meaning, through gauge and strings dynamics
February 07, 2024 16:36 - 1 hour - 1.65 GB VideoI will discuss the statistical physics of random growth processes which, on the one hand, model the non-perturbative gauge dynamics, emergence of space geometry in string theory on the other, yet could also model the evolution of language(s).
Emergent cosmology from quantum gravity: the universe as a quantum condensate
February 07, 2024 16:36 - 1 hour - 1.24 GB VideoThe construction of a quantum theory of gravity remains an open problem despite decades of efforts. In time, the very perspective on this problem evolved. From quantising General Relativity, the goal is now mostly understood to be unraveling a more fundamental microstructure of spacetime, based on non-geometric building blocks, and to show how spacetime and matter emerge as effective, approximate notions. Given some candidate building blocks, the task becomes analogous to that of extracting t...
Entanglement in complex quantum systems: From quantum information to many-body systems and back
February 07, 2024 16:36 - 1 hour - 1.27 GB VideoSommerfeld Theory Colloquium
Ergodicity, Entanglement and Many-Body Quantum Dynamics in Localization
February 07, 2024 16:36 - 1 hour - 1.09 GB VideoDo quantum many-body systems necessarily come to thermal equilibrium after a long enough time evolution? The conventional wisdom has long been that they do and that, in the process, any quantum information encoded in the initial state is lost irretrievably. Thus the dynamics of many-interacting particles becomes effectively classical. But these ingrained notions of thermalization and ergodicity have recently been called into question. In this talk I will discuss how ergodicity can break down ...
Cascade of phase transitions near Quantum Critical Point
February 07, 2024 16:36 - 1 hour - 1.03 GB VideoIn the standard picture of a quantum phase transition, a single quantum critical point separates the phases at zero temperature. Here we show that the two-dimensional case is considerably more complex. Instead of the single point separating the antiferromagnet from the normal metal, we have discovered a broad region between these two phases where the magnetic order is destroyed but certain areas of the Fermi surface are closed by a large gap. This gap reflects the formation of a novel quantum...
Arnold Sommerfeld Theory Colloquium
February 07, 2024 16:36 - 1 hour - 548 MB VideoThe next generation of surveys, e.g. the Dark Energy Survey, PanSTARRS, LSST, Euclid and others, aim to study the nature of Dark Energy and alternatives. The talk will discuss how the Dark Energy paradigm evolved over the past 20 years, and the cosmic probes which will help us to test it. In particular the surveys rely on accurate of photometric redshifts for the determination of cosmological quantities such as Dark Energy parameters and neutrino masses. The talk will describe photometric red...
Fantastic periods and where to find them
February 07, 2024 16:36 - 1 hour - 507 MB VideoAfter 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 t...
From Bell's theorem to Quantum Networks
February 07, 2024 16:36 - 1 hour - 1.05 GB VideoThe question, whether a local, realistic theory can be a valid description of nature led to Bell's formulation of a clear cut experimental test. In spite of the many measurements performed and the numerous violation of Bell's inequality, all these tests relied on assumptions opening loopholes for local realistic theories. We present experiments which attempted to close as many as possible loopholes during the recent years, and what still might be left to do. In the experiment, as Bell's inequ...
From Emergent Gravity to Dark Energy and Dark Matter
February 07, 2024 16:36 - 1 hour - 1.03 GB VideoThe observed deviations from the laws of gravity of Newton and Einstein in galaxies and clusters can logically speaking be either due to the presence of unseen dark matter particles or due to a change in the way gravity works in these situations. Until recently there was little reason to doubt that general relativity correctly describes gravity in all circumstances. In the past few year insights from black hole physics and string theory have lead to a new theoretical framework in which the gr...
From materials science to basic physics
February 07, 2024 16:36 - 1 hour - 966 MB VideoCondensed 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.
Functional renormalization group approach to correlated fermion systems
February 07, 2024 16:36 - 1 hour - 1.6 GB VideoThe functional renormalization group (RG) is an ideal tool for dealing with the diversity of energy scales and competition of instabilities in interacting fermion systems. Starting point is an exact flow equation which yields the gradual evolution from a microscopic model action to the effective low-energy action as a function of a continuously decreasing energy scale. Expanding in powers of the fields yields an exact hierarchy of flow equations for vertex functions. Truncations of this hiera...
Gauge Theories and Non-Commutative Geometry
February 07, 2024 16:36 - 1 hour - 1.1 GB VideoWe shall review the attempts to extend the quantum mechanical property of non-commutativity from phase space to ordinary space. These attempts took a more precise form in the case of gauge theories for which some concrete results have been obtained. In flat space they amount to a reformulation of the theory which looks interesting but they have not given so far any novel physical results. However, the introduction of gravity gives a richer structure and may offer some new insights.
Gone with the wind: The demise of protoplanetary discs and the birth of planets
February 07, 2024 16:36 - 1 hour - 1.06 GB VideoProtoplanetary 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...
Harmony of Scattering Amplitudes and Form Factors
February 07, 2024 16:36 - 1 hour - 1.14 GB VideoIn this seminar I will describe some of the hidden structures recently discovered in the scattering amplitudes of elementary particles, such as those measured at the Large Hadron Collider. These structures are responsible for the mysterious simplicity of these quantities, which is completely obscured by a calculation based on textbook techniques such as Feynman diagrams. I will then move on to discuss form factors. These are slightly off-shell quantities and, similarly to amplitudes, are also...
Higher Spin --- CFT duality
February 07, 2024 16:36 - 1 hour - 1 GB VideoThe conjectured relation between higher spin theories on anti de-Sitter (AdS) spaces and weakly coupled conformal �field theories is reviewed. I shall then outline the evidence in favour of a concrete duality of this kind, relating a speci�c higher spin theory on AdS3 to a family of 2d minimal model CFTs. Finally, I shall explain how this relation �ts into the framework of the familiar stringy AdS/CFT correspondence.
Higher-Spin Gravity and Higher Spin Black Holes in Three Dimensions
February 07, 2024 16:36 - 1 hour - 1.13 GB VideoThree-dimensional Einstein gravity has no local dynamical degree of freedom. Yet, it is far from being trivial when the cosmological constant is negative. (i) It admits black hole solutions. (ii) It easily allows for consistently interacting and tractable higher-spin extensions. (iii) It possesses remarkable asymptotic properties at infi�nity where an infi�nite-dimensional symmetry algebra emerges. These features make three-dimensional gravity a perfect "theoretical laboratory" in which to ex...
Is Dark Matter made of Primordial Black Holes? JWST might tell!
February 07, 2024 16:36 - 57 minutes - 352 MB VideoSommerfeld Theory Colloquium
How a physical system can be turned into a self-learning machine
February 07, 2024 16:36 - 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?
February 07, 2024 16:36 - 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
February 07, 2024 16:36 - 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
February 07, 2024 16:36 - 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
February 07, 2024 16:36 - 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
February 07, 2024 16:36 - 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...
Lattice QCD in Regensburg
February 07, 2024 16:36 - 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...