2014/15


Speaker (affiliation)

Title

Abstract

September

24




October 
1

Dmytro Volin 
Classification of unitary representations of su(n,mk) Lie superalgebras 
It is well known how to classify all unitary representations of compact algebras su(n) and su(nm), as well as all highestweight unitary representations of noncompact su(n,m) case. However, quite surprisingly, the generic su(n,mk) situation was not properly understood except for special choices of n,m,k.
In this talk I will cover this gap and give the full classification of the unitary representations. All of them appear to be of highestweight type, but with some weights being continuous rather than discrete. Despite this continuity in the spectrum we are still able to realise all representations using oscillators and therefore to prove the classification theorem easily. The resulting answer can be depicted in terms of generalised Young diagram inside the socalled Thook which originally was proposed in the context of AdS/CFT integrability.


8





15

Laine, Mikko (U. of Bern)

Can heavy ion collision experiments teach us something about cosmology?

Both heavy ion collision experiments and cosmology offer examples of
relativistic plasmas in which some particle species are out of equilibrium.
The outofequilibrium particles play little role for bulk thermodynamic
properties such as the overall pressure of the system, but are of vital
importance as observable 'relics' from the thermal epoch. In this talk
some basic concepts of outofequilibrium thermodynamics are reviewed,
and the question posed in the title is pondered with the example
of dark matter in cosmology versus heavy quarks in hot QCD.


22

Stefanski, Bogdan 
Holographic integrability for AdS3/CFT2 
The AdS3/CFT2 correspondence is one of the earliest known examples of holographic duality. It is an example of holography which involves the renormalisation group flow of a nonconformal gauge theory; it features prominently in the discussion of blackhole entropy computations as well as offering a definition of quantum invariants in a variety of geometrical settings.
I will review recent progress in using integrable methods to understand the planar limit of the AdS3/CFT2 correspondence. I will present the complete nonperturbative Smatrix for the worldsheet excitations of the string theory. In particular I will show how to incorporate massless modes into this description  something that, until now, has been a major stumbling block in the integrability approach. 

29

Anosh Joseph (DESY Zeutchen)

Supersymmetry on a Spacetime Lattice: Recent Developments

Several classes of supersymmetric theories can be discretized on a Euclidean lattice by preserving at least one supersymmetry exact at finite lattice spacing. I will detail the lattice formulations of supersymmetric gauge theories with four, eight and sixteen supercharges, with and without matter. Having a firstprinciples definition of supersymmetric gauge theories, through lattice discretization, would provide a window into their nonperturbative sectors. I will also briefly describe the Monte Carlo techniques used to study these theories at strong coupling.

November

12

Waldemar Schulgin 
Asymptotic symmetry group of the flat space string theory

Abstract: I will explain how to obtain the asymptotic symmetry group
of the target space from the worldsheet perspective. I will review the
AdS3 case and explain what are the difficulties to take the zero limit
of the cosmological constant. I will realize the asymptotic symmetry
group of threedimensional flat space (BMS3group) in terms of vertex
operators on the string worldsheet. Motivated by the BMS3 construction I will discuss vertex operators associated with spacetime diffeomorphisms in flat space string theory, and compute their algebra, which is a diffeomorphism algebra with higher derivative
corrections. 

19

Mukund Rangamani

Quantum entanglement and holography

Abstract: I will review the holographic methods to compute entanglement entropy. In particular, I will focus on general properties that the holographic construction must satisfy such as causality, respecting entropy inequalities etc..Time permitting I will describe other measures of quantum information and the clues they might hold for holography.


26

Epelbaum, Evgeny (Bochum)

CANCELLED







December 
3

Della Morte, Michele (Odensee)








January 
14 
Cristophe Royon (Saclay)

Forward Physics with tagged Protons at the LHC 
After defining diffraction in particle physics, we will describe briefly some of the physics topics that can be studied at the LHC using tagged protons, namely QCD and the structure of the pomeron in terms of quarks and gluons, as well as the search for extradimensions in the universe via anomalous couplings between photon, W and Z. We will finish the seminar by describing briefly the new detectors that will be installed to achieve these measurements.


21 
Evgeny Epelbaum (Bochum)

What Holds the World Together? Modern Theory of Nuclear Forces

Chiral effective field theory provides a powerful theoretical tool to
describe nuclear
forces and lowenergy reactions in fewnucleon systems. Recently, a
discretized version
of this approach has been developed, which allows one to access heavier
systems by
using Monte Carlo simulations to describe propagation in Euclidean time.
I will outline
the foundations of both the continuum and discretized formulations and
discuss selected
applications focusing, in particular, on the light quark mass dependence
of nuclear
observables. 

28

Pelaez, Jose

confirmed


February

4

Gabor Takacs 
Form factors in finite volume with applications 
Finite size effects play an important role in quantum field theory and its applications to statistical physics and lattice field theory. In this talk we present the description of the volume dependence of local operator matrix elements in 1+1 dimensional integrable field theories. Beyond the formal aspects, the finite volume form factors have important applications. In numerical approaches to field theory (lattice field theory, truncated conformal space approach) they enable the evaluation of infinite volume matrix elements, giving us access to interesting quantities such as e.g. resonance widths, and provide a testing ground for diverse versions of the form factor bootstrap approach. In terms of analytic methods they can be utilized to regulate spectral expansions, leading to the construction of a systematic expansion of correlators in thermal and other mixed states, and several other interesting results. Recently they also proved very useful in applying field theory to the study of nonequilibrium process initiated by quantum quenches.


6
Special time: 2pm Friday

Erik Verlinde 
Symmetric Product CFT’s and The Hawking Page Transition 
For symmetric product CFT’s the free energy can be calculated in a grand canonical ensemble in which one introduces a chemical potential for the central charge of the CFT. The result turns out to be symmetric in the chemical potential and the inverse temperature. It is well known that CFT's with a gravity duals exhibit a Hawking Page transition at fixed central charge when the temperature exceeds a critical value.
For symmetric product CFT’s there is a similar transition at fixed energy when the chemical potential falls below a critical value. In this talk I will discuss the physical interpretation of this transition, and comment on its possible generalization to other type of CFT’s.


6
Special time: 3:30pm Friday

Nikita Nekrasov 
Nonperturbative DysonSchwinger equations in N=2 susy gauge theories 
We study nonlocal symmetries of quantum field theory which relate topologically distinct sectors of the field space. In the context of the BPS/CFT correspondence, using the qqcharacters observables, we derive an infinite set of DysonSchwingertype relations, including the KnizhnikZamolodchikov(Bernard) equations, and BelavinPolyakovZamolodchikov equations, obeyed by the supersymmetric partition functions of N=2 gauge theory in the presence of Omegadeformation and defects. The qqcharacters generalize the qcharacters of quantum affine algebras and Yangians.


11

Romuald Janik 
String field theory, integrability and OPE coefficients 
In this talk I would like to describe why the problem of
finding OPE coefficients in N=4 SuperYangMills theory
is very challenging and discuss an approach through
string interactions described by the string field theory
vertex. All previous constructions of the string field theory
vertex were restricted to free worldsheet theory.
I will discuss a novel approach applicable in principle
to any interacting but integrable worldsheet theory.


18

Zohar Komargodski 
The Casimir Energy in FourDimensional Conformal Field Theories. 
Abstract: "Critical 1+1 dimensional systems on a circle have a ground state energy proportional to the central charge $c$. We study the analogous problem of 3+1 dimensional Conformal Field Theories on a ThreeSphere. This question also has a natural interpretation in the context of AdS/CFT, where the ground state energy is related to the mass of the AdS vacuum

March

4

Jan Plefka 
Quantum Gravity and the Stability of the Higgs Vacuum

A central outcome of the recent Higgs discovery is that the Standard Model (SM) appears to be a selfconsistent quantum field theory all the way up to the
Planck scale. Moreover, the measured values for the Higgs and top masses have an intriguing consequence for the question of stability of the Higgs
vacuum: The SM lies close to the border of absolute electroweak vacuum stability and metastability. However, these celebrated results extrapolate the SM into a region
where quantum gravity effects become important. We have therefore computed the quantum gravitational contributions to the standard model effective potential and
analyzed their effects on the Higgs vacuum stability in the framework of effective field theory. Nonrenormalizability of Einstein gravity induces higher dimension
operators at the one loop level with novel couplings \eta_{1/2}. We find that the true minimum of the standard model effective potential now lies below the Planck scale for almost
the entire parameter space (\eta_{1/2}(mt) > 0.01). In addition quantum gravity is shown to contribute to the minimal value of the standard model NLO effective potential at the percent level.
The quantum gravity induced contributions yield a metastable vacuum for a large fraction of the parameter space in the flowing couplings \eta_{1/2}.


11





25

Sergei Alexandrov 
Nonpertrubatie effects in string theory compactifications

I'll review the current understanding of the low energy effective theory resulting from compactifications of Type II superstrings on CalabiYau manifolds. The effective action can be encoded into the metric on a moduli space which is known to receive quantum stringy corrections, both perturbative and nonperturbative. I'll show how the nonperturbative geometry of this moduli space can be described using twistorial techniques. In the end, I'll argue that the instanton effects coming from NS5branes, whose understanding is still very incomplete, might be related to a quantization of a certain integrable structure.

April 
1 
Gleb Arutyunov 
Integrable deformations of the AdS5 × S5 superstring and mirror duality

Doing a double Wick rotation in the worldsheet theory of the light cone AdS_5 x S^5 superstring results in an inequivalent, socalled mirror theory that plays an important role in solving the AdS/CFT spectral problem. Departing from an integrable deformation
of the AdS_5 x S^5 string sigmamodel, I show that this mirror theory can be interpreted as the light cone theory of a free string albeit on a different background.

May 
25 *CANCELLED* 
Thomas Creutzig

Sigma models and selfdual vertex super algebras 
Mathieu moonshine relates one of the exceptional finite simple groups, the Mathieu group M_24, to string theory on K3 surfaces. It has been understood by John Duncan and collaborators that the unique extremal selfdual super vertex algebra of central charge 12 is closely related to this story.
The first half of the talk, I plan to review Mathieu moonshine, then I want to explain how in general selfdual vertex algebras relate to full twodimensional bulk conformal field theories and especially Duncan's super vertex algebra relates directly to a special sigma model on K3 




