# Abstracts for Rivière-Fabes Symposium on Analysis and PDE

April 20-22, 2007

**All talks in Vincent Hall 16**

### Carlos Kenig

Lecture 1 - The Energy Critical, Focusing, Non-Linear Schrödinger and Wave Equations

Abstract 1: We will discuss a point of view on obtaining optimal global well-posedness and scattering results for critical dispersive and wave equation problems. The program applies to both focusing and defocusing problems. The specific applications of the method to be discussed are to the focusing, energy critical non linear Schrodinger and wave equations. The method is a blend of ideas from elliptic and parabolic problems, with oscillatory integral techniques. This is joint work with Frank Merle.

### Juan Luis Vazquez

Lecture 1 - The Theory of Fast Diffusion Equations. Main features and recent news.

Abstract 1: We will review the main mathematical features of the nonlinear heat °ow called the Fast Diffusion Equation δtu = Δum, m < 1. Much is known nowadays about this flow, posed inRn, in a bounded open subset or on a manifold. Surprising phenomena appear, like loss of regularity (solutions with Lp initial data may not be bounded), extinction in finite time, even lack of existence or lack of uniqueness for classes of small and smooth initial data.

As novelties, we will present geometrical results related to the 2-d Ricci °ow and the description of asymptotics using weighted functional inequali- ties of Hardy-Sobolev type.

Background Reference:J. L. Vázquez. "Smoothing and Decay Estimates for Nonlinear Diffusion Equations. Equations of Porous Medium Type", Oxford Lecture Notes in Maths. and its Applications 33, Oxford University Press, 2006.

### Pierre Raphael

Lecture 1 - Blow up for some nonlinear dispersive PDE's

Abstract 1: The focusing nonlinear Schrodinger equation iut +Δu+ u|u|p-1 = 0 inRN is a universal model for the self trapping of waves in a nonlinear medium. The cases p = 3 and N = 2,3 are of particular physical relevance but are quite different from the mathematical point of view. The phenomenon we aim at describing is the concentration of the nonlinear wave which mathematical counterpart is the finite time blow up of the solution to the Cauchy problem. A general understanding of the singularity formation for NLS is still widely open.

I will start by reviewing the series of results obtained in collaboration with Frank Merle for the L2 critical NLS iut + Δu + u|u|4/N = 0 in RN and which prove the existence and stability of "log-log" type blow up scenario. I will then explan how these results may be extended to various situations and in particular provide tools to construct new blow up solutions in the L2 super critical setting. I will also explain how the intuition based on the use of Liouville type classification theorem has recently allowed us to prove the blow up of the critical norm in super critical settings.

I will conclude by presenting a recent work joint with Mohammed Lemou anf Florian Mehats which concerns the quite unexpected adaptation of these techniques to nonlinear kinetic Vlasov-Poisson type problems emerging from astrophysiscs.

### Ovidiu Savin

Lecture 1 - Symmetry of global solutions to certain fully nonlinear elliptic equations

Abstract 1: We consider bounded global solutions to fully nonlinear equations of the type $F(D^2u)=f(u)$. The main assumption on $F$ and $f$ is that there exists a one dimensional solutions $g$ that solves the equation in all directions. We show that solutions with Lipschitz level sets depend on one variable, that is the level sets are in fact hyperplanes. In the particular case when $F=\triangle$ and $f(u)=u3-u$ the same result was obtained by Barlow, Bass and Gui by probabilistic methods.

### Sylvia Serfaty

Lecture 1 - Vortices in the 2D Ginzburg-Landau model with magnetic field.

Abstract 1: We review some results obtained jointly with Etienne Sandier on the Ginzburg-Landau model of superconductivity in 2 dimensions, and described in our recent book. In a superconducting sample, according to the intensity of the applied field, phase transitions happen and vortices appear in certain regimes. By studying energy minimizers in a suitable parameter regime, we extract limiting problems that describe the optimal repartition of vortices according to the applied field. We will also describe some of our more recent results on the subject.

*Background Reference:* Etienne Sandier, Sylvia Serfaty, Vortices in the Magnetic Ginzburg-Landau Model, Progress in Nonlinear Differential Equations 70, Birkhauser, 2007.

### Alexander Volberg

Lecture 1 - Equation of Monge-Ampère and Bellman Solutions for Certain Harmonic Analysis Problems (After Slavin-Stokolos)

Abstract 1: Bellman function method in Harmonic Analysis was introduced by Donald Burkholder for finding the norm in L^p of martingale transform. Later it became clear that scope of the method is relatively wide, in particular Nazarov-Treil-Volberg obtained by this method a necessary and sufficient condition for the two weight martingale transform to be bounded (which was used then in Bellman estimates of Ahlfors-Beurling transform by Petermichl and myself). Recently Slavin and Stokolos made an important observation how Monge-Ampère equation may help to find the exact Bellman function of certain Harmonic Analysis problems. They illustrated their idea by finding the elegant and short way to find the Bellman function of dyadic maximal operator (A. Melas' recent result). We will illustrate this approach by this and couple of other examples, where Monge-Ampère allows us to find exact Bellman function of a Harmonic Analysis problem. In particular, to find best constants and extremal functions (or extremal sequences).