October  2, 2014
Geometry and Model Theory Seminar 2014-15
at the Fields Institute

Organizers: Ed Bierstone, Patrick Speissegger


The idea of the seminar is to bring together people from the group in geometry and singularities at the University of Toronto (including Ed Bierstone, Askold Khovanskii, Grisha Mihalkin and Pierre Milman) and the model theory group at McMaster University (Bradd Hart, Deirdre Haskell, Patrick Speissegger and Matt Valeriote).

As we discovered during the programs in Algebraic Model Theory Program and the Singularity Theory and Geometry Program at the Fields Institute in 1996-97, geometers and model theorists have many common interests. The goal of this seminar is to further explore interactions between the areas. It served as the main seminar for the program on O-minimal structures and real analytic geometry, which focussed on such interactions arising around Hilbert's 16th problem.

The seminar meets once a month at the Fields Institute,

Upcoming Seminars
October 2, 2014
Stewart Library


Ethan Jaffe, University of Toronto
Pathological phenomena in Denjoy-Carleman classes

We provide explicit constructions of three functions in the theory of Denjoy-Carleman classes. First, generalizing a classical result and a result of Rolin, Speissegger, and Wilkie, we construct a function in any given Denjoy-Carleman class which is nowhere in any smaller one. Second, we also construct a function which is formally of a given Denjoy-Carleman class at every point, but is not actually in the class. Third, we construct a smooth example of function quasianalytic of a given Denjoy-Carleman class on every curve in that class, but which fails to actually be in the class.

3:30- 4:40 pm

André Belotto, University of Toronto
Local monomialization of a system of First Integrals

We consider a non-singular analytic manifold M and a singular foliation F with N analytic globally defined first integrals (f_1,... f_N). We present a monomialization of these first integrals. More precisely, for each point P in M, there exists a finite collection of local blowings-up G_i:(M_i,F_i) ->(M,F) covering P, such that the singular foliation F_i has N monomial first integrals at every point, i.e. at each point Q_i of M_i, there exists a coordinate system u=(u_1,...,u_m) and N monomial first integrals (u^{a1}, ..., u^{aN}) of F_i such that the exponents a1,..., aN are linearly independent.
Past Seminars
July 31, 2014
Stewart Library

2:00-3:00 pm

Tamara Servi, Centro de Matemática e Aplicações Fundamentais
Multivariable Puiseux Theorem for convergent generalised power series

The classical Puiseux Theorem says that the solutions y=g(x) of a real analytic equation f(x,y)=0 in a neighbourhood of the origin are convergent Puiseux series. The aim of my talk is to extend this result, and its multivariable version, to the class of convergent generalised power series. A generalised power series (in several variables) is a series with real nonnegative exponents whose support is contained in a cartesian product of well-ordered subsets of the real line. Let A be the collection of all convergent generalised power series. I will show that, if f(x_1,...,x_n,y) is in A, then the solutions y=g(x_1,...,x_n) of the equation f=0 can be expressed as terms of the language which has a symbol for every function in A and a symbol for division. This result extends to other classes of functions definable in polynomially bounded o-minimal expansions of the real field, such as quasianalytic Denjoy-Carleman classes, Gevrey multisummable series and a class containing some Dulac Transition Maps of real analytic planar vector fields.

3:30- 4:40 pm

Jean-Philippe Rolin, Université de Bourgogne
Formal embeddings of transseries into flows

This work is inspired by some results about the fractal analysis of the orbits of a diffeomorphism in one variable. In order to perform a similar analysis for an extended class, we prove a normal form result and the embedding into a flow for a diffeomorphism given by a transseries (joint work with P. Mardesic, M. Resman and V. Zupanovic).

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