seminar FisMat

FisMat Seminar, August 14, 15:45

Speaker: Rafael Tiedra de Aldecoa. Pontificia Universidad Católica de Chile

Title: Ruled Strips With Asymptotically Diverging Twisting

Place: Pontificia Universidad Católica, Facultad de Matemáticas, Campus San Joaquin, Sala 5

Abstract:
We consider the Dirichlet Laplacian in a 2-dimensional strip composed of segments translated along a straight line with respect to a rotation angle with velocity diverging at infinity. We show that this model exhibits a “raise of dimension” at infinity leading to an essential spectrum determined by an asymptotic 3-dimensional tube of annular cross section. If the cross section of the asymptotic tube is a disc, we also prove the existence of discrete eigenvalues below the essential spectrum. Joint work with David Krejcirik (Prague).

Seminar Spectral Theory and PDE

Seminar Spectral Theory and PDE, June 27, 17:00

Speaker: Leonid Parnovski. University College London

Title: Floating mats and sloping beaches: spectral asymptotics of the Steklov problem on polygons.

Place: PUC Chile, Campus San Joaquin, Fac. Matematicas, Sala 2

Abstract:
I will discuss recent results (joint with M.Levitin, I.Polterovich and D.Sher) on the asymptotic behaviour of Steklov eigenvalues on polygons and other two-dimensional domains with corners. The answer is completely unexpected and depends on the arithmetic properties of the angles. 

Seminar Spectral Theory and PDE

Seminar Spectral Theory and PDE, June 6, 17:00

Expositor:  Horia Cornean, Aalborg University

Title:  Peierls’ substitution for low lying spectral energy windows 

Abstract: We consider a 2d periodic Schrödinger operator for which we assume that either the first Bloch eigenvalue remains isolated while its corresponding Riesz spectral projection family has a non-zero Chern number, or the first two Bloch eigenvalues have a conical crossing. The system is afterwards  perturbed by a weak magnetic field which slowly varies around a positive mean. Then we prove the appearance of a “Landau type” structure of spectral islands and gaps both at the bottom of the spectrum, and near the possible crossings.
This is joint (past and ongoing) work with B. Helffer (Nantes) and R. Purice (Bucharest).

http://www.mat.uc.cl/~graikov/seminar.html

seminar FisMat

FisMat Seminar, June 5, 15:45

Speaker: Horia Cornean. Aalborg University

Title: A Beals criterion for magnetic pseudo-differential operators proved with magnetic Gabor frames

Place: Pontificia Universidad Católica, Facultad de Matemáticas, Campus San Joaquin, Sala 5

Abstract:
First, we give a new proof for the Beals commutator criterion for non-magnetic Weyl pseudo-differential operators based on classical Gabor tight frames. Second, by introducing a modified ‘magnetic’ Gabor tight frame, we naturally derive the magnetic analogue of the Beals criterion originally considered by Iftimie-Mantoiu-Purice. This is joint work with Bernard Helffer (Nantes) and Radu Purice (Bucharest). https://doi.org/10.1080/03605302.2018.1499777

Seminar Spectral Theory and PDE

Seminar Spectral Theory and PDE, May 30, 17:00

Speaker: Dmitrii Shirokov. National Research University Higher School of Economics, Russia

Title: On Constant Solutions of Su(2) Yang-Mills Equations

Place: Pontificia Universidad Católica, Facultad de Matemáticas (Campus San Joaquin), Sala 2

Abstract:
We present all constant solutions of the Yang-Mills equations with SU(2) gauge symmetry for an arbitrary constant non-Abelian current in Euclidean space of arbitrary finite dimension. We use the singular value decomposion method and the method of two-sheeted covering of orthogonal group by spin group to do this. Using hyperbolic singular value decomposition, we solve the same problem in arbitrary pseudo-Euclidean space. The case of Minkowski space is discussed in details. Nonconstant solutions of the Yang-Mills equations are considered in the form of series of perturbation theory.

http://www.mat.uc.cl/~graikov/seminar.html 

seminar FisMat

FisMat Seminar, May 29, 15:45

Speaker: Andrés Fernando Reyes Lega. Universidad de los Andes (Colombia)

Title: Emergent Gauge Symmetries, Quantum Operations and Anomalies

Place: Pontificia Universidad Católica, Facultad de Matemáticas (campus San Joaquin), Sala 5

Abstract:
The Gelfand-Naimark-Segal (GNS) construction is a fundamental tool for the study of the representation theory of operator algebras. It also plays a prominent role in the algebraic approach to quantum field theory. In this talk I will discuss some examples of applications of the algebraic approach to quantum physics to systems with a finite number of degrees of freedom. I will illustrate how the GNS construction naturally leads to interesting connections between gauge symmetries, anomalies and quantum-information concepts like entanglement entropy and quantum operations.

Seminar Spectral Theory and PDE

Seminar Spectral Theory and PDE, May 16, 17:00

Frédéric Klopp. Institut de Mathématiques Jussieu – Paris Rive Gauche, Sorbonne
Title: Exponential decay for the 2 particle density matrix of disordered many-body fermions at zero and positive temperature.
Place: Pontificia Universidad Católica de Chile, Facultad de Matemáticas (campus San Joaquin), Sala 2
Abstract:
We will consider a simple model for interacting fermions in a random background at zero and positive temperature. At zero temperature, we prove exponential decay for the 2 particle density matrix of a ground state. At positive temperature we prove exponential decay for the 2 particle density matrix of the density operator in the grand canonical ensemble.
http://www.mat.uc.cl/~graikov/seminar.html

Announcement, conference

2nd JNMP Conference on Nonlinear Mathematical Physics: 2019

The 2nd JNMP Conference on Nonlinear Mathematical Physics: 2019 conference is held from May 26 till June 4, 2019 at the University of Santiago de Chile.
USACH – Centro de estudios de postgrado y educación continua 
(Center for postgraduate studies and continuing education) 
Piso 3, Av. Apoquindo 4499, Las Condes, Región Metropolitana, Santiago, Chile

Description

This conference is being organized for the Journal of Nonlinear Mathematical Physics (JNMP) community. We aim to bring together experts and young scientists in the area of Mathematical Physics that concern Nonlinear Problems in Physics and Mathematics. The main topic of the conference is centered around the scope of JNMP: continuous and discrete integrable systems including ultradiscrete systems, nonlinear differential- and difference equations, applications of Lie transformation groups and Lie algebras, nonlocal transformations and symmetries, differential-geometric aspects of integrable systems, classical and quantum groups, super geometry and super integrable systems.

seminar FisMat

FisMat Seminar, May 15, 15:45

Massimo Moscolari. Aalborg University
Title: Beyond Diophantine Wannier diagrams: gap labelling for Bloch-Landau Hamiltonians
Place: Pontificia Universidad Católica, Facultad de Matemáticas (Campus San Joaquin), Sala 5
Abstract:
In 1978 Wannier discovered a Diophantine relation expressing the integrated density of states of a gapped group of bands of the Hofstadter Hamiltonian as a linear function of the magnetic field flux with integer slope. I will show how to extend this relation to a gap labelling theorem for any 2D Bloch-Landau Hamiltonian operator and to certain non-covariant systems having slowly varying magnetic fields. The integer slope will be interpreted as the Chern character of the projection onto the space of occupied states. The talk is based on a joint work with H. Cornean and D. Monaco.

Seminar Spectral Theory and PDE

Seminar Spectral Theory and PDE, May 2, 17:00

Georgi Raikov. Pontificia Universidad Católica de Chile
Title: Threshold singularities of the spectral shift function for geometric perturbations of a magnetic Hamiltonian
Place: Pontificia Universidad Católica de Chile, Facultad de Matemáticas (campus San Joaquin), Sala 2
Abstract:
I will consider the 3D Schrödinger operator H0 with constant magnetic field, and its perturbations H_+ (resp., H_-\, ) obtained from H_0  by imposing Dirichlet (resp., Neumann) conditions on an appropriate surface. I will introduce the Krein spectral shift function for the operator pairs (H_0;H_+) and (H_0;H_-), and will discuss its singularities at the Landau levels which play the role of thresholds in the spectrum of the unperturbed operator H_0
The talk is based on a joint work with V. Bruneau (Bordeaux).
http://www.mat.uc.cl/~graikov/seminar.html