8 Mar
2011
TU Wien

Florian Preis (TU Wien)

Inverse magnetic catalysis in dense holographic matter
Abstract:
We study the chiral phase transition in a magnetic field at finite
temperature and chemical potential within the SakaiSugimoto model, a
holographic topdown approach to QCD with a large number of colors. We
consider the limit of a small separation of the flavor D8branes, which
corresponds to a dual field theory comparable to a NambuJona Lasinio
(NJL) model. Mapping out the surface of the chiral phase transition in
the parameter space of magnetic field strength, quark chemical
potential, and temperature, we find that for small temperatures the
addition of a magnetic field decreases the critical chemical potential
for chiral symmetry restoration  in contrast to the case of vanishing
chemical potential where, in accordance with the familiar phenomenon of
magnetic catalysis, the magnetic field favors the chirally broken
phase. This "inverse magnetic catalysis" (IMC) appears to be associated
with a previously found magnetic phase transition within the chirally
symmetric phase that shows an intriguing similarity to a transition
into the lowest Landau level. We estimate IMC to persist up to $10^{19}
G$ at low temperatures.

15 Mar
2011
Uni Wien

Pascal Anastasopoulos (TU Wien)

Living in a world of strings
Abstract:
We will review the basic ideas on how the Standard Model can be
realized as an Open String vacuum and we will analyze some
phenomenological implications of such realization.

22 Mar
2011
TU Wien

Paul Erker (Uni Wien)

Genuine Multipartite Entanglement in Dicke States
Abstract:
Genuine multipartite entanglement has witnessed serious attention
within the scientific community recently. It was found to play a role
in
various fields, from solid state phase transitions to biological
systems, and to be an important resource for e.g. quantum computation
or
quantum secret sharing. Dicke states represent an important class of
multipartite quantum states, which e.g. appear as ground states of
Hamiltoneans in various systems. Criteria to detect genuine
multipartite entanglement in such states were recently developed and
will be
presented.

29 Mar 2011
Uni Wien

Thomas Zojer (TU Wien)

Three dimensional gravity and logarithmic conformal field theories Abstract: Threedimensional massive gravity has been extensively studied in the last years as a toy model for quantum gravity.
It is simple enough to find 'solutions', e.g. propagating degrees of freedom, gravitons, or other interesting ingredients
like black holes. An important tool is the gauge gravity duality, or AdS/CFT correspondence, which in the context of
threedimensional quantum gravity is easily tractable since a lot is known about two dimensional CFTs. I am going to
address special deformations of gravity theories and discuss the respective changes on the CFT side that lead to the
conjecture of AdS/LCFT, i.e. some gravity theories are dual to socalled logarithmic conformal field theories.

5 Apr 2011
TU Wien

Ivan Coluzza (Uni Wien)

A coarsegrained approach to protein design: learning from design to understand folding
Abstract:
Computational studies have given a great contribution in building our
current understanding of the complex behavior of protein molecules;
nevertheless, a complete characterization of their free energy
landscape still represents a major challenge. Here, we introduce a new
coarsegrained approach that allows for an extensive sampling of the
conformational space of a large number of sequences. We explicitly
discuss its application in protein design, and by studying four
representative proteins, we show that the method generates
sequences with a relatively smooth free energy surface directed towards
the target structures.

12 Apr 2011
Uni Wien

Harald Oberhofer (TU München)

Predicting electron transfer rates (with computer simulations)
Abstract:
We show the feasibility of using computer simulations to calculate
electron exchange reaction rates in extended systems from scratch.
We achieve this by determining the dependence of all parameters
occurring in the Marcus theory rate expression on the distance $r$ of
Donor and Acceptor. Using both, classical and density functional theory
(DFT) simulation techniques
we calculate the reorganisation energy $\lambda(r)$ and the electronic
transition matrix element $H_\text{ab}(r)$. Together with the potential
of mean force $G(r)$ as a function $r$ this allows us
to calculate the overall reaction rate. We also take into account
quantum corrections due to the classical nature of the vibrational
modes in our model.
We illustrate this approach with our results for the Ru$^{2+}$ 
Ru$^{3+}$ electron selfexchange reaction in water, which are in good
agreement with experiment.
Also we show preliminary results for a large modifiedfullerene
cluster, a system of high relevance to modern organic solar cells.

3 Mai 2011
TU Wien

Denise Lorenz (Uni Wien)

LPVs in NGC147 and NGC185  Probing a new tool to measure extragalctic distances
Abstract:
Most of the variable stars change their brightness periodically and can
therefore be classified according to their periods and amplitudes. Of
special interest are variables that increase their mean luminosity
according to the length of their period, as has been found for Cepheid
stars. They can be used to establish a periodluminosityrelation (PLR)
which enables us to determine the distance just by measuring the period
of the star. Huge surveys of variable stars in the Magellanic Clouds 
the neighbourhood of the Milky Way  revealed sequences of Long Period
Variables (LPVs) in a periodluminositydiagram. These findings
encouraged the search of a PLR valid for LPVs and the investigation of
its universality.
LPVs are intrinsically brighter than Cepheid variables, hence, at
greater distances LPVs are still observable. Therefore, a universal
LPVPLR would allow to measure distances of all stellar systems in
which we are able to detect LPVs.
Meanwhile, technical progress allows to resolve single stars in
galaxies not only in the surroundings of the Milky Way but also at a
distance of the Andromeda Galaxy and beyond. Our work describes the
search of LPVs in the two neighbouring dwarf galaxies of Andormeda,
NGC147 and NGC185, and their use in order to establish a universal PLR.

10 Mai
2010
Uni Wien

Florian Hebenstreit (Uni Graz)

Quantum kinetics of nonperturbative electronpositron production  The influence of temporal and spatial inhomogeneities
Abstract:
Nonperturbative electronpositron pair creation in electric fields
(Schwinger effect) has been a longstanding but still unobserved
prediction of QED. Due to the advent of a new generation of
highintensity laser systems such as the European XFEL or the Extreme
Light Infrastructure (ELI) it might, however, become possible to
observe this effect within the next decades. Previous investigations
led to a good understanding of the general mechanisms behind the pair
creation process, however, realistic electric fields as they might be
present in upcoming experiments have not been fully considered yet. In
this talk I focus on various aspects of the Schwinger effect in the
presence of inhomogeneous electric fields: First, I consider the pair
creation process in the presence of a spatially homogeneous,
timedependent electric field. Most notably, the momentum distribution
of created particles in the presence of a pulsed electric field
with subcycle structure, which serves as a simple model of the
timedependence of a realistic laser pulse, is presented. Moreover, I
introduce a formalism by means of which the Schwinger effect in the
presence of space and timedependent electric fields can be treated
properly. Finally, I present the time evolution of various observable
quantities (charge distribution, momentum spectrum, number of created
particles) in the presence of a simple space and timedependent
electric field which have been calculated for the first time.

17 Mai
2011
TU Wien

Michal Michalčík (TU Wien)

Stringy effects in the AdS/CFT correspondence
Abstract:
Even though the AdS/CFT correspondence is originally formulated via
string theory, most of its aspects were investigated in the string
theory low energy limit  the Supergravity. It is therefore of
interrest to look for stringy effects. There are two essential
ingredients to describe a conformal field theory : the spectrum of
conformal weights and coefficients of the threepoint functions of
primary operators. The latter one causes more problems in the string
context, since the computational methods based on the AdS/CFT
correspondence are (mostly) restricted to the operators dual to
supergravity fields. I will present a method to calculate correlation
functions of a class of operators with large Rcharges which are dual
to classical string states at strong coupling.

24 Mai
2011
Uni Wien

Jan Kurzidim (TU Wien)

Glass formation of colloids in porous media
Abstract:
We have studied a fluid of hard spheres that evolves in the presence of
randomlyplaced hardsphere obstacles. In particular, we are interested
in the prolongation of the fluid's structural relaxation, i.e. in the
formation of a glass phase. Using molecular dynamics simulations, we
found two arrest mechanisms: the localization of fluid particles is
dominant at high obstacle densities, $\phi_m$, whereas mutual blocking
among the fluid particles prevails at large fluid densities, $\phi_f$.
Similar effects have been shown to play vital roles in real systems
like the movement of proteins in the cytoplasm of living cells. Upon
varying $\phi_m$ and $\phi_f$, we unveiled very different scenarios of
dynamic arrest, anomalous diffusion, and the presence of multiple
nontrivial time scales in the system. To elucidate these phenomena, we
geometrically distinguished the pores formed by the obstacles, which
enabled us to identify particles located (a) in the percolating
backbone of accessible space and (b) in pores of finite volume. We
separately evaluated various characteristics for particles in (a) and
(b) and demonstrated that they exhibit significant differences.

31 Mai
2011
TU Wien

Jan Schlemmer (Uni Wien)

Local thermal equilibrium in relativistic quantum field theory
Abstract:
In the description of spatially extended physical systems one often
assigns to them thermal quantities (temperature, pressure, ...) varying
in space and time. While there is a well established theory
(statistical mechanics) for linking the thermodynamic description of
systems with constant temperature ("global equilibrium") to microscopic
models, for the case of varying thermal parameters the situation is
much less clear cut and in fact there are many proposed frameworks to
link the microscopic and macroscopic level. In my talk I will present a
framework especially suited for relativistic quantum field theory, talk
about its generalization to quantum fields on curved spacetime and try
to summarize some results obtained for specific systems, both on flat
and curved spacetime.

7 Jun 2011
Uni Wien

Renate Pazourek (TU Wien)

Attosecond physics  Ultrafast electron dynamics in atoms
Abstract: With the ability to control and shape infrared laser fields and the generation of isolated
attosecond light pulses by high harmonic generation a new research field ? attoscience 
was born about ten years ago. Since then it has become possible to study electron dynamics
in atoms, molecules and solids on it's natural time scale.
After a general introduction to attosecond physics I will focus on ultrafast electron
dynamics in atoms, in particular correlated electron dynamics in helium for which the
timedependent Schr¿dinger equation can still be solved numerically. I will present
simulations for twophoton double ionization of helium and compare some of the calculated
results with experiments. In addition, I will give an introduction to attosecond
streaking, a pumpprobe technique using an ultrashort extreme ultaviolet pulse and a
synchronized IR laser field, which allows to extract time shifts between different
photoionization events with attosecond precision.

21 Jun 2011
TU Wien

Andrea Puhm (CEASaclay Paris)

Black Hole Microstates
Abstract: A century after the first black hole solution to Einstein's equation was found black holes remain an intense and puzzling
area of research. While general relativity is a very good description far away from the black hole horizon quantum mechanical
effects like Hawking radiation are present close to the horizon leading to apparent inconsistencies like information loss. A
theory of quantum gravity is needed in order to describe black holes in full glory and to resolve these puzzles. In this talk
I will introduce how black holes can be described in string theory and how ''black hole microstates'' may cure these
paradoxes. Constructing such microstates is a difficult task and so far they have been found only for extremal
(supersymmetric and nonsupersymmetric) black holes. I will present a new approach that enabled us to find microstates
corresponding to nonextremal (nonsupersymmetric) black holes, thus taking a step forward to a stringy description of
realistic black holes.
