Sommerfeld Theory Colloquium (ASC)

Sommerfeld Theory Colloquium, I describe the physics of black holes and show how the traditional

approach leads to the information paradox. I will then discuss some

of the proposed resolutions and the difficulties they need to overcome.

I then discuss soft black hole hair and describe how it may help to

resolve the information paradox. Finally, I will review the problems

that still need to be overcome.

Sommerfeld Theory Colloquium, Highest resolution Event Horizon Telescope (EHT) observations will

probably soon tell us more about the supermassive black hole at

the Galactic Centre (Sgr A*) and the cores of active galactic nuclei

(AGN). It might also help to clarify the long-standing question

whether the central massive objects in AGN are instead close pairs

of black holes. Mergers of supermassive black hole pairs would provide

the strongest gravitational wave signals. I will present examples

of how we identify potential close binary black hole candidates

based on the combined analysis of high resolution radio interferometric

(VLBI) observations and multi- wavelength data. I will also

provide an outlook on the scientific prospects with regard to future

EHT-observations.

Sommerfeld Theory Colloquium, In 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 called ”frustration”. It leads to a complex

energy ”landscape” with many valleys separated by barriers, so

simple algorithms easily get trapped in local minima which have a

higher energy than the global minimum. Many problems in science,

and engineering are formulated as optimization problems. In quantum

annealing one tries to avoid being trapped in a local minimum by

adding quantum fluctuations so the system can tunnel to regions of

lower energy. The strength of the quantum fluctuations is gradually

reduced to zero during the annealing schedule. This method applies

to problems with binary variables, known as qubits in the quantum

case. There is considerable interest in AQC at present, in large part

because a company, D-Wave, has produced an actual device, the latest

version of which has about one thousand qubits. In addition,

there has been considerable theoretical work mainly using computer

simulations to see if there is a ”quantum speedup” compared with

analogous classical algorithms in which thermal, rather than quantum,

fluctuations are used to escape from local minima. In the talk

I will discuss difficulties in obtaining a quantum speedup due to (i)

(quantum) phase transitions that the system can undergo during the

annealing schedule, and (ii) the sensitivity of the state of the system

to the precise values of the interactions, i.e. chaos. A related chaotic

effect is that the state of the system can change dramatically with

small changes in the temperature (temperature-chaos), for thermal

annealing, and the strength of the quantum fluctuations, for quantum

annealing.

Sommerfeld Theory Colloquium, Low-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.

Sommerfeld Theory Colloquium, Metals 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 arise in the low energy description of such states,

which are still very poorly understood. I will focus on the paradigmatic

problem of a metal coupled to fluctuations of a critical Ising

order parameter and discuss unexpected scaling properties at finite

temperature.

Sommerfeld Theory Colloquium, 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.

Sommerfeld Theory Colloquium, 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.

Sommerfeld Theory Colloquium

Sommerfeld Theory Colloquium, New Physics searches at the LHC are mostly being performed with

the aim of detecting new states. A complementary strategy is to

look for new interactions, something that typically involves precise

measurements. In this talk I argue how many of the current SM (and

BSM) measurements in the top sector could be used to efficiently and

consistently determine of the couplings of an effective field theory and

in particular that of the SM at dimension 6.

Sommerfeld Theory Colloquium, Do 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 in disordered quantum systems through

the phenomenon of many-body localization. In contrast to thermalizing

fluids, quantum correlations can persist through time evolution

of the localized state even at high energy densities. Thus, investigating

the many-body localization transition offers a concrete route

to address fundamental unsolved questions concerning the boundary

between classical and quantum physics in the macroscopic world. I

will emphasize the important role that quantum entanglement plays

in current attempts to understand this fascinating dynamical phase

transition. Finally I will present recent progress in confronting the

emerging theoretical understanding of many-body localization with

experimental tests using systems of ultra-cold atoms.