Dec 2017 
 Tuesday 19th at 10:00  Seminar  
Colloquium (at ULg) 
Colloquium in honor of the 64th Birthday of P. Lecomte 
Abstract  info: click here 
Location  Département de Mathématique de l'ULg, Building B37, Grande traverse 12, Sart Tilman, Liège 

 Monday 18th at 10:00  Seminar  
Colloquium (at ULg) 
Colloquium in honor of the 64th Birthday of P. Lecomte 
Abstract  info: click here 
Location  Département de Mathématique de l'ULg, Building B37, Grande traverse 12, Sart Tilman, Liège 

Jun 2017 
 Wednesday 21st at 15:00  Seminar  
Roman Riser (Holon Institute of Technology (Israel)) 
TBA 
Location  CYCL07, Marc de Hemptinne, LLN 

Apr 2017 
 Thursday 20th at 15:00  Seminar  
Jules Lamers (Chamlers) 
The structure in the temperate region of the Fmodel with domainwall boundaries 
Abstract  The Fmodel for 'antiferroelectric' materials is a special case (a = b < c) of the sixvertex model from classical statistical physics. Domain walls are a particularly interesting choice of boundary conditions that allow for a lot of analytic control, both at finite size and for macroscopically large systems. To complement results obtained using quantum integrability and other techniques, R. Keesman and I have performed a numerical (MonteCarlo) study for moderate system size, up to L = 512. Our data are perfectly consistent with known exact results, and uncover an intricate structure in the 'temperate region' of the lattice. In this seminar I will give a whiteboard introduction to the model and everything that is needed in order to appreciate the pictures that I will present towards the end. Based on arXiv:1702.05474 and ongoing research.... [±] 
Location  CYCL09B, Marc de Hemptinne, LLN 

 Thursday 6th at 15:00  Seminar  
Kristina Schubert ((University of Muenster)) 
Wigner's semicircle law for random matrices with dependent entries 
Abstract  Wigner's semicircle law states that the spectral distribution of random
matrices with independent entries converges to the semicircle
distribution. Since its original version, proved by Wigner in the 1950s, there have
been a number of generalization of this statement for various random
matrix ensembles. We review some more recent results about the validity of this law for
matrices with dependent entries. In particular, we consider matrices,
where the matrix entries are given by a stochastic process with decaying
correlations. In this case, the way we fill the stochastic process into
the matrix, determines whether the limiting spectral distribution is the
semicircle or not.... [±] 
Location  CYCL09B, Marc de Hemptinne, LLN 

Mar 2017 
 Thursday 30th at 15:30  Seminar  
Jean Liénardy (UCLouvain) 
The XXZ spin chain: dynamic supersymmetry and special scalar products 
Abstract  We consider the quantum spin ½ XXZ chain with anisotropy parameter â= 1/2 and open boundary conditions. This model possesses a dynamic supersymmetry on the lattice. We explicitly compute the cohomology of the corresponding supercharge and show it is nontrivial for specific diagonal boundary interactions. This implies that the Hamiltonian possesses zeroenergy ground states which are supersymmetry singlets. We use the supersymmetry to determine sum rules for special scalar products involving an arbitrary number of these supersymmetry singlets for chains of different lengths. We compute their scaling limit and compare our results to the predictions of conformal field theory.
This talk is based on ongoing work with C. Hagendorf.
... [±] 
Location  CYCL07, M.deHemptinne, LLN 

 Thursday 23rd at 15:00  Seminar  
Ananya Ghatak (IIScBangalore) 
Dealing with nonHermitian quantum systems 
Location  CYCL09B, Marc de Hemptinne, LLN 

Feb 2017 
 Wednesday 22nd at 15:00  Seminar  
Thimothée Thiery (KULeuven) 
Randomwalks in timedependent random environment and the KPZ universality class: the Beta polymer 
Abstract  The KPZ universality class in 1+1D is a remarkable example of universality in outofequilibrium statistical mechanics. 'KPZtype’ scaling and fluctuations are indeed observed in a variety of statistical mechanics model, ranging e.g. from outofequilibrium growth to interacting particle systems, but also in some modern experiments. The directed polymer (DP) problem, that is the equilibrium statistical mechanics of directed paths in a random environment, is also believed to be in the KPZ universality class for a large choice of random environments. In a recent paper [1] Barraquand and Corwin introduced the Beta polymer, a Bethe ansatz exactly solvable model of DP on the square lattice which has the peculiarity of being equivalent to a model of random walk in a onedimensional dynamic random environment (TDRWRE). This is due to a special choice of shortrange correlations of the random environment that encodes an additional conservation law (compared to the usual DP problem): the conservation of probability. Interestingly, the analysis of the statistical properties of the TDRWRE cumulative distribution function (in the original BC paper [1]), and transition probability (in a recent paper by myself and Pierre Le Doussal [2]), suggest that: (i) the TDRWRE nature of the Beta polymer breaks KPZ universality in the diffusive regime of the random walk; (ii) the DP nature of the TDRWRE can still be observed and KPZ universality is found in the large deviations regime of the random walk. The Beta polymer thus shed a new light on both the DP and TDRWRE problems. In this talk I will present the known results on and around the Beta polymer, focusing mostly on the techniques used in [2].
[1] G. Barraquand and I. Corwin, arXiv:1503:04117, Probab. Theory Relat. Fields (2016).
[2] T. Thiery and P. Le Doussal, arXiv:1605.07538, JPhysA (2016).... [±] 
Location  CYCL09B, Marc de Hemptinne, LLN 

 Friday 17th at 14:00  Seminar  
Laure SaintRaymond (ENS Lyon) 
Irreversibility in gas dynamics 
Abstract  At the atomistic level, a gas can be described by a (reversible) Hamiltonian system of ODEs (the Newton equations). However the macroscopic evolution of a gas (described by the Boltzmann equation) has an entropy which is an increasing function of time, and is therefore irreversible.
The goal of this lecture is to point out where the irreversibility shows up in the derivation of the Boltzmann equation from the Newton equations.... [±] 
Location  ULB, Salle des Professeurs, 9th Floor, Building NO 

 Wednesday 15th at 15:00  Seminar  
Andreas Klümper (U. Wuppertal) 
Thermodynamics, contact and density profiles of the repulsive GaudinYang model 
Abstract  We address the problem of computing the thermodynamic properties of the
repulsive onedimensional twocomponent Fermi gas with contact interaction
(GaudinYang model). We derive an exact system of only two nonlinear integral
equations for the thermodynamics of the homogeneous model. This system allows
for an easy and extremely accurate calculation of thermodynamic properties
circumventing the difficulties associated with the truncation of the
thermodynamic Bethe ansatz system of equations. We present extensive results
for the densities, polarization, magnetic susceptibility, specific heat,
interaction energy, Tan contact and local correlation function of opposite
spins. Our results show that at low and intermediate temperatures the
experimentally accessible contact is a nonmonotonic function of the coupling
strength. As a function of the temperature the contact presents a pronounced
local minimum in the TonksGirardeau regime which signals an abrupt change of
the momentum distribution in a small interval of temperature. The density
profiles of the system in the presence of a harmonic trapping potential are
computed using the exact solution of the homogeneous model coupled with the
local density approximation. At finite temperature the density profile
presents a double shell structure (partially polarized centre and fully
polarized wings) only when the polarization in the center of the trap is above
a critical value.
... [±] 
Location  CYCL08, Marc de Hemptinne, LLN 
