Sommerfeld Theory Colloquium (ASC)

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.

Sommerfeld Theory Colloquium, All flows show a transition from a laminar phase to a turbulent one for sufficiently high flow speeds. In many cases turbulence develops in a succession of instabilities that create flows of increasing temporal and spatial complexity (Lord Rayleigh, Sommerfeld, Heisenberg, Taylor, Landau etc), For the classroom example of pipe flow and

several other flows, the linear stability analysis of the laminar profile does not reveal any instability, so that the very first point in that cascade of instabilities is absent. Over the last decade much of the mystery of the transition in pipe flow has been resolved, primarily

thanks due to suitable adaptations and extensions of ideas from nonlinear dynamics. Numerical and experimental data corroborate a scenario where the appearance of new classes of fully 3d solutions and their increasing entanglement provides the key ingredients for the transition. Further studies on the spatio-temporal dynamics in the transition region, where turbulence is not space-filling, reveal

intriguing similarities to the directed percolation transition in statistical

mechanics.

Sommerfeld Theory Colloquium, 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.

Sommerfeld Theory Colloquium, We 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 technological limits of these measurements.

Sommerfeld Theory Colloquium, I will review the basic defi�nitions and ideas of the twistor program

for fundamental physics, as started by Roger Penrose around 1970. I

will give particular attention to certain conformally invariant struc-

tures involving deformed helicities, relevant to scattering amplitudes

for massless �elds. These played a role in Penrose's earliest contour

integral expressions, but have more recently been rediscovered and

greatly developed as an approach to regularization.