## Montreal Analysis Seminar

Seminars are usually held on Mondays or Fridays at Concordia,
McGill or Universite de Montreal

For suggestions, questions etc. please contact Dmitry Jakobson
(jakobson@math.mcgill.ca), Iosif Polterovich
(iossif@dms.umontreal.ca) or
Alina Stancu (alina.stancu@concordia.ca)

## FALL 2016

** Friday, September 16, 13:30-14:30, McGill, Burnside 920**

**Jeff Galkowski** (CRM/McGill)

A Quantitative Vainberg Method for Black Box Scattering

** Abstract: **
We give a quantitative version of Vainberg’s method relating pole
free regions to
propagation of singularities for black box scatterers. In particular, we
show that there is a
logarithmic resonance free region near the real axis of size t with
polynomial bounds on the
resolvent if and only if the wave propagator gains derivatives at rate t.
Next we show that if
there exist singularities in the wave trace at times tending to infinity
which smooth at rate t, then
there are resonances in logarithmic strips whose width is given by t. As
our main application
of these results, we give sharp bounds on the size of resonance free
regions in scattering on
geometrically nontrapping manifolds with conic points. Moreover, these
bounds are generically
optimal on exteriors of nontrapping polygonal domains.

** Monday, October 3, UdeM, 14:00-15:00, U. Montreal,
Pav. Andre Aisenstadt, Room 5448**

**Alexandre Girouard** (Laval University)

Discretization and Steklov eigenvalues of compact manifold with boundary

** Abstract: **
Let M be a compact n-dimensional Riemannian manifolds with cylindrical
boundary, Ricci curvature bounded below by k and injectivity radius bounded
below by r. We introduce a notion of discretization of the manifold M,
leading to a graph with boundary which is roughly isometric to M , with
constant depending only on k, r, n. In this context, we prove a uniform
spectral comparison inequality between the Steklov eigenvalues of the
manifold M and those of its discretization. Some applications to the
construction of sequences of surfaces with boundary of fixed length and
with large Steklov eigenvalues are given. In particular, we obtain such a
sequence for surfaces with connected boundary. These applications are based
on the construction of graph-like surfaces which are modeled using
sequences of graphs with good expansion properties. This talk is based on
joint work with Bruno Colbois (Neuchatel) and Binoy Raveendran.

** Friday, October 28, Concordia, 14:00, LB 921-4**

**Scott Rodney** (Cape Breton university)

The Poincare Inequality and the $p$-Laplacian

** Abstract: **
In this talk I will explore a necessary and sufficient condition for the
validity of a Poincar\'e - type inequality.
This work will be presented in the context of the degenerate Sobolev
spaces $W^{1,p}_Q(\Omega)$ and the Degenerate
$p$-Laplacian given by $\Delta_p u =
\text{Div}\Big( \Big|\sqrt{Q(x)}\nabla u(x)\Big|^{p-2} Q(x)
\nabla u\Big)$ where
$Q(x)$ is a non-negative definite $L^1_{\text{loc}}$ matrix valued function.

** Special Analysis/Applied seminar**

** Friday, October 28, McGill, 15:30-16:30, Burnside 1120**

** Daniel Han-Kwan** (Ecole Polytechnique)

The quasineutral limit of the Vlasov-Poisson system

**Abstract: ** We shall review a few recent results about the
quasineutral limit of the Vlasov-Poisson system.
This is a singular limit in which the Poisson equation degenerates and
which gives rise to singular non-linear PDEs that are ill-posed in general.

** Friday, November 4, McGill, Burnside 920, 13:30-14:30**

**Carlos Perez** (BCAM, Bilbao)

Rough Singular Integrals: A1 theory

** Abstract:**
In this mostly expository talk we will discuss new results for rough
Singular Integral Operators involving $A_1$ weights. These are convolution
operators whose kernels do not satisfy the standard regularity conditions
(Lipschitz or Dini). Being more precise we will discuss estimates for
these operators in the context of weighted $L^p$ spaces with weights
satisfying the $A_1$ condition. These results are known since the 80's
(work of Duoandikoetxea y Rubio de Francia) for $A_p$ weights but we found
quantitative estimates in the context of the special class of $A_1$. Most
probably these results are far from satisfactory and we will discuss some
open problems.

This is a joint work with I. Rivera-Rios and L. Roncal.

** Monday, November 7, McGill, Burnside 920, 14:00-15:00**

**Steve Lester** (CRM and McGill)

Quantum unique ergodicity for half-integral weight automorphic forms

** Abstract:**
Given a smooth compact Riemannian manifold (M, g) with no boundary an
important problem in Quantum Chaos studies the distribution of L^2 mass of
eigenfunctions of the Laplace-Beltrami operator in the limit as the
eigenvalue tends to infinity. For M with negative curvature Rudnick and
Sarnak have conjectured that the L^2 mass of all eigenfunctions
equidistributes with respect to the Riemannian volume form; this is known
as the Quantum Unique Ergodicity (QUE) Conjecture. In certain arithmetic
settings QUE is now known. In this talk I will discuss the analogue of QUE
in the context of half-integral weight automorphic forms. This is based on
joint work Maksym Radziwill.

** Friday, November 11, Burnside 920, 13:00-14:00**

**Michael Hitrik** (UCLA)

Spectra for non-selfadjoint operators and integrable dynamics

**Abstract: ** Spectra for non-selfadjoint operators often display
fascinating features, from lattices of eigenvalues for operators of
Kramers-Fokker-Planck type to eigenvalues for operators with analytic
coefficients in dimension one, concentrated to unions of curves. In this
talk, we shall discuss spectra for non-selfadjoint perturbations of
selfadjoint semiclassical operators in dimension 2, assuming that the
classical flow of the unperturbed part is completely integrable. We give
complete asymptotic expansions for all individual eigenvalues in
suitable regions of the complex spectral plane, close to the edges of
the spectral band. It turns out that those eigenvalues have the form of
the "legs in a spectral centipede" and are generated by suitable
rational flow-invariant Lagrangian tori. This is joint work with
Johannes Sjostrand.

** Friday, November 11, Burnside 920, 14:00-15:00**

**Katya Krupchyk** (UC Irvine)

$L^p$ bounds on eigenfunctions for operators with double
characteristics

** Abstract:**
Starting with the pioneering works of Hormander and Sogge, the
question of establishing uniform and, more generally, $L^p$ estimates
for eigenfunctions of elliptic self-adjoint operators in the high energy
limit has been of fundamental significance in spectral theory and
applications. In this talk, after a brief introduction to this circle of
questions, we shall discuss $L^p$ bounds on the ground states for a
class of semiclassical operators with double characteristics, including
some Schrodinger operators with complex-valued potentials. Sharp
bounds are obtained under the assumption that the quadratic
approximations along the double characteristics are elliptic. This is a
joint work with Gunther Uhlmann.

** Monday, November 21, 13:30-14:30, Burnside 920**

**Matthieu Leautaud** (Paris and Montreal)

Quantitative unique continuation and intensity of waves in the shadow
of an obstacle
** Abstract:** The question of global unique continuation is the
following: Does the observation of the wave intensity on a little subdomain
during a time interval (0,T) determine the total energy of the wave? In an
analytic context, this question was solved in 1949 by the well-know
Holmgren-John theorem; in the "smooth case", it was finally tackled by
Tataru-Robbiano-Zuily-Hörmander in the nineties. After a review of these
results, we shall describe the quantitative unique continuation estimate
associated to the qualitative theorem of Tataru-Robbiano-Zuily-Hörmander,
that is, give the optimal logarithmic stability result. In turn, this
estimate yields the optimal a priori bound on the penetration of waves
into the shadow region, as well as the cost of approximate controls for
the wave equation. This is joint work with Camille Laurent.

** Monday, December 12, (date and time to be confirmed), Room TBA**

**Thierry Daude** (Cergy-Pontoise)

Non-uniqueness results for the anisotropic Calderon problem with data
measured on disjoint sets.
** Abstract:**
In this talk, we shall give some simple counterexamples to uniqueness
for the anisotropic Calderon problem on Riemannian manifolds with boundary
when the Dirichlet and Neumann data are measured on disjoint sets of the
boundary. We provide counterexamples in the case of two and three
dimensional Riemannian manifolds with boundary having the topology of
circular cylinders in dimension two and toric cylinders in dimension three.
The construction could be easily extended to higher dimensional Riemannian
manifolds. This is joint work with Niky Kamran (McGill University) and
Francois Nicoleau (Université de Nantes).

## WINTER 2017

## SUMMER 2016

** Thursday, June 2, 13:30-14:30, Concordia, Room LB 921-04
**

**Vlad Yaskin** (University of Alberta, Edmonton)

Stability results for sections of convex bodies

** Abstract:**
(pdf)
Let $K$ be a convex body in $\mathbb R^n$.
The parallel section function of $K$ in the direction $\xi\in S^{n-1}$ is
defined by
$$
A_{K,\xi}(t)=\mathrm{vol}_{n-1}(K\cap \{\xi^{\perp}+t\xi\}), \quad
t\in \mathbb R.
$$
If $K$ is origin-symmetric (i.e. $K=-K$), then Brunn's theorem implies
$$
A_{K,\xi}(0) =\max_{t\in \mathbb R} A_{K,\xi}(t)
$$
for all $\xi\in S^{n-1}$.
The converse statement was proved by Makai, Martini and \'Odor.
Namely, if $A_{K,\xi}(0) =\max_{t\in \mathbb R} A_{K,\xi}(t)$ for all
$\xi\in S^{n-1}$, then $K$ is origin-symmetric.
We provide a stability version of this result. If $A_{K,\xi}(0)$ is
close to $\max_{t\in \mathbb R} A_{K,\xi}(t)$ for all $\xi\in
S^{n-1}$, then $K$ is close to $-K$.
Joint work with Matthew Stephen.

** Monday, August 1, 13:30-14:30, McGill, Burnside 920 (room
to be confirmed) **

**Fedor Pakovich** (Ben Gurion University)

On semiconjugate Rational Functions

** Abstract: ** pdf

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