Seminars and Colloquia by Series

Tuesday, November 28, 2017 - 13:00 , Location: Skiles 006 , Ian Jauslin , IAS, Princeton , , Organizer: Federico Bonetto
In 1979, O. Heilmann and E.H. Lieb introduced an interacting dimer model with the goal of proving the emergence of a nematic liquid crystal phase in it. In such a phase, dimers spontaneously align, but there is no long range translational order. Heilmann and Lieb proved that dimers do, indeed, align, and conjectured that there is no translational order. I will discuss a recent proof of this conjecture. This is joint work with Elliott H. Lieb.
Tuesday, November 28, 2017 - 11:00 , Location: Skiles 006 , Vieri Mastropietro , Universita' di Milano, Italy , , Organizer: Federico Bonetto
Abstract: A number of quantities in quantum many-body systems show remarkable universality properties, in the sense of exact independence from microscopic details. I will present some rigorous result establishing universality in presence of many body interaction in Graphene and in Topological Insulators, both for the bulk and edge transport. The proof uses Renormalization Group methods and a combination of lattice and emerging Ward Identities.
Friday, November 17, 2017 - 15:00 , Location: Skiles 006 , Timo Weidl , Univ. Stuttgart , , Organizer:

This is part of the 2017 Quolloquium series.

Starting from the classical Berezin- and Li-Yau-bounds onthe eigenvalues of the Laplace operator with Dirichlet boundaryconditions I give a survey on various improvements of theseinequalities by remainder terms. Beside the Melas inequalitywe deal with modifications thereof for operators with and withoutmagnetic field and give bounds with (almost) classical remainders.Finally we extend these results to the Heisenberg sub-Laplacianand the Stark operator in domains.
Thursday, November 16, 2017 - 13:30 , Location: Skiles 006 , Lotfi Hermi , Florida International University , , Organizer:

This is part of the 2017 Quolloquium series.

We use the weighted isoperimetric inequality of J. Ratzkin for a wedge domain in higher dimensions to prove new isoperimetric inequalities for weighted $L_p$-norms of the fundamental eigenfunction of a bounded domain in a convex cone-generalizing earlier work of Chiti, Kohler-Jobin, and Payne-Rayner. We also introduce relative torsional rigidity for such domains and prove a new Saint-Venant-type isoperimetric inequality for convex cones. Finally, we prove new inequalities relating the fundamental eigenvalue to the relative torsional rigidity of such a wedge domain thereby generalizing our earlier work to this higher dimensional setting, and show how to obtain such inequalities using the Payne interpretation in Weinstein fractional space. (Joint work with A. Hasnaoui)
Tuesday, November 7, 2017 - 13:00 , Location: Skiles 006 , Günter Stolz , University of Alabama, Birmingham , , Organizer: Michael Loss
Tuesday, November 7, 2017 - 10:00 , Location: Skiles 006 , Yulia Karpeshina , University of Alabama, Birmingham , , Organizer: Michael Loss
  Existence of ballistic transport for Schr ̈odinger operator with a quasi- periodic potential in dimension two is discussed. Considerations are based on the following properties of the operator: the spectrum of the operator contains a semiaxis of absolutely continuous spectrum and there are generalized eigenfunctions being close to plane waves ei⟨⃗k,⃗x⟩ (as |⃗k| → ∞) at every point of this semiaxis. The isoenergetic curves in the space of momenta ⃗k corresponding to these eigenfunctions have a form of slightly distorted circles with holes (Cantor type structure). 
Friday, October 27, 2017 - 15:00 , Location: Skiles Room 202 , Rafael Benguria , Catholic University of Chile , , Organizer: Michael Loss
During the last few years there has been a systematic pursuit for sharp estimates of the energy components of atomic systems in terms of their single particle density. The common feature of these estimates is that they include corrections that depend on the gradient of the density. In this talk I will review these results. The most recent result is the sharp estimate of P.T. Nam on the kinetic energy. Towards the end of my talk  I will present some recent results concerning geometric estimates for generalized Poincaré inequalities obtained in collaboration with C. Vallejos and H. Van Den Bosch. These geometric estimates are a useful tool to estimate the numerical value of the constant of Nam's gradient correction term.
Tuesday, March 28, 2017 - 15:00 , Location: Skiles 005 , Alissa Geisinger , University of Tuebingen, Germany , , Organizer: Michael Loss
We consider the two-dimensional BCS functional with a radial pair interaction. We show that the translational symmetry is not broken in a certain temperature interval below the critical temperature. For this purpose, we first introduce the full BCS functional and the translation invariant BCS functional. Our main result states that theminimizers of the full BCS functional coincide with the minimizers of the translation invariant BCS functional for temperatures in the aforementioned interval. In the case of vanishing angular momentum our results translate to the three dimensional case. Finally, we will explain the strategy and main ideas of the proof. This is joint work with Andreas Deuchert, Christian Hainzl and Michael Loss.
Tuesday, March 14, 2017 - 15:00 , Location: Skiles 005 , Tobias Ried , Karlsruhe Institute of Technology , , Organizer: Michael Loss
We study regularity properties of weak solutions of the homogeneous Boltzmann equation. While under the so called Grad cutoff assumption the homogeneous Boltzmann equation is known to propagate smoothness and singularities, it has long been suspected that the non-cutoff Boltzmann operator has similar coercivity properties as a fractional Laplace operator. This has led to the hope that the homogenous Boltzmann equation enjoys similar smoothing properties as the heat equation with a fractional Laplacian. We prove that any weak solution of the fully nonlinear non-cutoff homogenous Boltzmann equation (for Maxwellian molecules) with initial datum $f_0$ with finite mass, energy and entropy, that is, $f_0 \in L^1_2(\R^d) \cap L \log L(\R^d)$, immediately becomes Gevrey regular for strictly positive times, i.e. it gains infinitely many derivatives and even (partial) analyticity.This is achieved by an inductive procedure based on very precise estimates of nonlinear, nonlocal commutators of the Boltzmann operator with suitable test functions involving exponentially growing Fourier multipliers.(Joint work with Jean-Marie Barbaroux, Dirk Hundertmark, and Semjon Vugalter)
Monday, November 14, 2016 - 15:00 , Location: Skiles 005 , Tobias Kuna , Unisrsity of Reading, UK , Organizer: Federico Bonetto
The discrete truncated moment problem considers the question whether given a discrete subsets $K \subset \mathbb{R}$ and a sequence of real numbers one can find a measure supported on $K$ whose (power) moments are exactly these numbers. The truncated moment is a challenging problem. We derive a minimal set of necessary and sufficient conditions. This simple problem is surprisingly hard and not treatable with known techniques. Applications to the truncated moment problem for point processes, the so-called relizability or representability problem are given. The relevance of this problem for statistical mechanics in particular the theory of classic liquids, is explained. This is a joint work with M. Infusino, J. Lebowitz and E. Speer.