# Atelier de travail annuel du projet SINGSTAR 2017

Europe/Paris
Hôtel des Planchettes (Saint Flour)

### Hôtel des Planchettes

#### Saint Flour

7 Rue des Planchettes, 15100 Saint-Flour
Description

The workshop of the ANR project SINGSTAR for 2017 will take place in St. Flour, in the Cantal from the 6 to 9 november.

The main goal of the meeting will be to give a pleasant space for members of the project and their collaborators to work together, in the style of the famous Anogia workshop of 2014. There will be a few talks each day, but a lot of time set aside for discussion and work.

Transportation will be organized to and from Clermont-Ferrand:

• Clermont -> St. Flour : Sunday 5 November, leaving Clermont around 17:00.
• St. Flour -> Clermont : Friday 10 November, arriving Clermont around 11:00.

Accomodation will be at the Hôtel des Planchettes (home of the annual École d'Été de Probabilités, for those that know it).  Website: http://www.hotelrestaurantlesplanchettes.fr/

Participants
• Berthomieu Alain
• Claire Debord
• Dominique Manchon
• Elmar Schrohe
• Georges Skandalis
• Hervé Oyono-Oyono
• Iakovos Androulidakis
• Jean Renault
• Jean-Marie LESCURE
• Jérémy Mougel
• Karsten Bohlen
• Maria Paula Gomez Aparicio
• Michel Hilsum
• Nigel Higson
• Omar Mohsen
• Paolo Antonini
• Pierre Julg
• Robert Yuncken
• Rémi Côme
• Saad BAAJ
• Stephane Vassout
• Vito Felice Zenobi
• Yeong Chyuan Chung
• Monday, 6 November
• 09:00 09:50
The wave equation, scattering theory and the Bernstein transform 50m
I shall describe work in progress with Bob Yuncken and Tyrone Crisp. The Bernstein transform is a map from one function space to another, like the Fourier transform or the Radon transform. It is part of Bernstein’s theory of smooth representations of p-adic groups, but the version I’m going to discuss comes from the tempered representation theory of real groups such as SL(2,R). The main problem in either context is to prove that it exists! I’ll explain what the Bernstein transform is designed to do, how to characterize it, at least for SL(2,R), using scattering theory for a wave equation (this involves a geometric space that is very similar to the tangent groupoid) and why I think that eventually it will be best understood from the point of view of C*-algebra theory (for the moment we rely on constructions that only work for smooth subalgebras).
Speaker: Nigel Higson
• 10:00 10:20
pause 20m
• 12:30 13:30
Lunch 1h
• 16:00 16:20
pause 20m
• 18:00 18:50
à préciser 50m
Speaker: Pierre Julg
• 19:30 21:00
Dinner 1h 30m
• Tuesday, 7 November
• 09:00 09:50
Bounded $H^\infty$-calculus for Cone Differential Operators 50m
We model a conic manifold by a manifold $\mathbb B$ with boundary $\partial \mathbb B=:X$. In a collar neighborhood we introduce coordinates $(t,x)$, where $t$ is the distance to $\partial \mathbb B$ and $x$ the variable in $X$. A cone differential operator of order $\mu$ is an operator $A: C^\infty_c(\mathbb B^\circ)\to C^\infty_c(\mathbb B$ that can be written near $\partial \mathbb B$ in the form $$A=t^{-\mu}\sum_{k=0}^\mu a_k(t)(-t\partial_t)^k\quad \text{with }a_k\in C^\infty([0,1)\mathrm{Diff}^{\mu-k}(X)).$$ We consider an extension of $A$ in a weighted cone Sobolev space $\mathcal H^{s,\gamma}_p(\mathbb B)$ with domain $\mathcal D(A) = \mathcal H^{s+\mu,\gamma+\mu}_p(\mathbb B)\oplus \mathcal E$, where $\mathcal E$ is a space of asymptotics functions. Given a sector $$\Lambda_\theta= \{re^{i\phi}: r\ge0, \theta\le\phi\le2\pi-\theta\}, \quad 0<\theta<\pi,$$ we show that any extension of $A$ which is parameter-elliptic with respect to $\Lambda_\theta$ has a bounded $H^\infty$-calculus on $\mathbb C\setminus \Lambda_\theta.$ Parameter-ellipticity with respect to $\Lambda_\theta$ here requires the following \begin{enumerate} \item Denote by $\sigma_\psi^\mu(A)$ the principal symbol of $A$. Then $\sigma_\psi^\mu(A)-\lambda$ is invertible for $\lambda \in \Lambda_\theta$, even up to the boundary, if one takes into account the degeneracy. \item The principal conormal symbol $\sigma_M^\mu(A)(z)$ is invertible for all $z\in \mathbb C$ with ${\rm Re}\, z= \frac{n+1}2-\gamma -\mu$ or ${\rm Re}\, z= \frac{n+1}2-\gamma$. \item $\Lambda_\theta$ is a sector of minimal growth for the model cone operator $$\widehat A= t^{-\mu}\sum_{k=0}^\mu a_k(0)(-t\partial_t)^k$$ acting on cone Sobolev spaces over he infinite cone. \end{enumerate} Applications concern the Laplacian and the porous medium equation on manifolds with warped conical singularities. (Joint work with J\"org Seiler (Torino))
Speaker: Elmar Schrohe
• 10:00 10:20
pause 20m
• 12:30 13:30
Lunch 1h
• 16:00 16:20
pause 20m
• 17:00 17:50
Noncommutative completion and universality of Boutet de Monvel's algebra 50m
Given as data an embedding of certain singular manifolds, I will describe a procedure which associates to this data a $C^{\ast}$-algebra correspondence. Such a noncommutative completion of an embedding is functorial and universal. As a particular instance of this construction I will discuss Boutet de Monvel's algebra in the setting of singular manifolds.
Speaker: Karsten Bohlen
• 18:00 18:50
The injectivity radius of Lie manifolds 50m
Lie manifolds were introduced by Ammann, Lauter and Nistor. These are a large class of noncompact complete (Riemannian) manifolds well behaved for the study of index theory on noncompact spaces. Their geometric structure is described by a Lie algebra of vector fields on a suitable compactification with corners. Equivalently by a Lie algebroid over the compactification.In this talk we will present the main geometrical features of Lie manifolds. In particular we will explain how the theory of connections and their associated geodesic flow on Lie algebroids leads to the proof that every Lie manifold has uniformly positive injectivity radius, a result recently obtained in collaboration with G. De Philippis and N. Gigli.
Speaker: Paolo Antonini
• 19:30 21:00
Dinner 1h 30m
• Wednesday, 8 November
• 09:00 09:50
Smooth $K$-theory 50m
Smooth K-theory is defined on a smooth manifold as an extension of topological K-theory by differential forms. In the case of a proper submersion, direct image for smooth K-theory is defines using Bismut and al.'s eta-forms, which are differential forms entering in the transgression of the local families index theorem. The construction of a direct image in the case of a closed immersion should use corresponding objects which are currents instead of smooth differential forms.
Speaker: Alain Berthomieu
• 10:00 10:20
pause 20m
• 10:20 11:00
à préciser 40m
Speaker: Omar Moshen
• 12:30 13:30
Lunch 1h
• 16:00 16:20
pause 20m
• Thursday, 9 November
• 09:00 09:50
Revisiting the $K$-theory of $CP^n$ from a (singular) foliation viewpoint 50m
This is report on work in progress with Nigel Higson. We are exploring an idea which comes from a very simple observation: The Bruhat cells of various flag manifolds are exactly the orbits of the action by a nilpotent matrix group. So one might try to use the apparatus developed for singular foliations in order to address representation theory problems. Making a start with this, we look at the case of $CP^n$ and the action by triangular matrices. It turns out that the nilpotency of this group allows us to shed some geometric light in the well-known K-theory group of $CP^n$, using index theory and techniques developed with Georges Skandalis to split singularities. Using these techniques we also construct interesting $K$-theory elements.
Speaker: Iakovos Androulidakis
• 10:00 10:20
pause 20m
• 10:20 11:10
The $K$-theory of operator algebras on $L^p$ spaces 50m
I will recall the notion of quantitative $K$-theory for filtered $C^\ast$-algebras developed by Oyono-Oyono and Yu, and outline how it can be extended to a larger class of Banach algebras, including operator algebras on $L^p$ spaces. This then provides a tool for investigating the $K$-theory of $L^p$ analogs of crossed products or uniform Roe algebras in some work in progress that I will briefly describe. If time permits, I will also list a few general questions about the $K$-theory of operator algebras on $L^p$ spaces.
Speaker: Yeong Chyuan Chung
• 12:30 13:30
Lunch 1h
• 16:00 16:20
pause 20m
• 18:00 18:40
à préciser 40m
• 19:30 21:00
Dinner 1h 30m
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